Systems, methods and apparatuses for multiple access point (multi-AP) coordination in wireless local area networks (WLANS)

ABSTRACT

Methods and apparatuses are described herein for multiple AP coordination in wireless local area networks (WLANs). For example, a station (STA) may receive, from a first access points (APs), a probe response frame that includes one or more indicators indicating multiple AP operation capabilities of the first AP and a second AP. The STA may transmit, to at least one of the first AP or the second AP, a multiple AP association request frame that enables the first AP to be associated with the second AP for a multiple AP operation. The STA may receive, from the first AP, a first multiple AP association response frame indicating acceptance or rejection of the multiple AP operation with the first AP. The STA may receive, from the second AP, a second multiple AP association response frame indicating acceptance or rejection of the multiple AP operation with the second AP.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage, under 35 U.S.C. § 371, ofInternational Application No. PCT/US2019/060508 filed Nov. 8, 2019,which claims the benefit of U.S. Provisional Application No. 62/873,396,filed Jul. 12, 2019, U.S. Provisional Application No. 62/815,130, filedMar. 7, 2019, U.S. Provisional Application No. 62/790,738, filed Jan.10, 2019 and U.S. Provisional Application No. 62/757,507, filed Nov. 8,2018, the contents of which are hereby incorporated by reference herein.

BACKGROUND

In the existing wireless networks (e.g., WLAN) implemented by Instituteof Electrical and Electronics Engineers (IEEE) 802.11 standards, astation (STA) may send an association request to an access point (AP) towhich the STA would like to associate in order to establish theappropriate connection state. If the elements of the association requestmatch the capabilities of the AP, the AP sends an association responseto the STA to indicate that the STA is in a member of the basic serviceset (BSS) where the AP is associated with. In the existing wirelessnetworks, the STA merely exchanges the request and response frames toassociate with a single AP, but any support for the multiple APdiscovery and multiple AP association from a single STA is not provided.Thus, methods and apparatuses that enable a single STA to discovermultiple APs and associate with more than one AP are needed.

SUMMARY

Systems, methods and apparatuses are described herein for multiple AP(or multi-AP) coordination in wireless local area networks (WLANs). Forexample, a station (STA) may receive, from a first access point (AP), aprobe response frame that includes one or more indicators indicatingmultiple AP operation capabilities of the first AP and a second AP. Themultiple AP operation capabilities may comprise a multiple AP jointtransmission capability, a multiple AP hybrid automatic repeat request(HARQ) capability, a multiple AP multiple-input multiple-output (MIMO)capability, a dynamic AP selection capability, a multiple AP roamingcapability, or a multiple AP coordinated beamforming capability. The STAmay then transmit, to at least one of the first AP or the second AP, amultiple AP association request frame that enables the first AP to beassociated with the second AP for a multiple AP operation with the STA.Multiple AP operation may include reception of signals by the STA fromthe first AP and the second AP, for example, using coordinatedorthogonal frequency-division multiple access (OFDMA) or coordinatednulling. Upon transmitting the multiple AP association request frame,the STA may receive, from the first AP, a first multiple AP associationresponse frame that indicates acceptance or rejection of the multiple APoperation with the first AP. The STA may also receive, from the secondAP, a second multiple AP association response frame that indicatesacceptance or rejection of the multiple AP operation with the second AP.On a condition that both the first and second multiple AP associationresponse frames indicate acceptance, the STA may perform the multiple APoperation with the first AP and the second AP.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawings,wherein like reference numerals in the figures indicate like elements,and wherein:

FIG. 1A is a system diagram illustrating an example communicationssystem in which one or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram illustrating an example wirelesstransmit/receive unit (WTRU) that may be used within the communicationssystem illustrated in FIG. 1A according to an embodiment;

FIG. 10 is a system diagram illustrating an example radio access network(RAN) and an example core network (CN) that may be used within thecommunications system illustrated in FIG. 1A according to an embodiment;

FIG. 1D is a system diagram illustrating a further example RAN and afurther example CN that may be used within the communications systemillustrated in FIG. 1A according to an embodiment;

FIG. 2 is a diagram illustrating an example of coordinated orthogonalfrequency-division multiple access (OFDMA);

FIG. 3 is a diagram illustrating an example resource allocation forcoordinated OFDMA;

FIG. 4 is a diagram illustrating an example of coordinatednulling/coordinated beamforming;

FIG. 5 is a diagram illustrating an example of coordinatednulling/coordinated beamforming (CB/CN) using interference alignment;

FIG. 6 is a diagram illustrating an example of single user jointprecoded multiple access point (multi-AP) transmission or coordinatedsinger user (SU) beamforming;

FIG. 7 is a diagram illustrating an example of multi-user joint precodedmultiple AP transmission or coordinated multi user (MU) beamforming;

FIG. 8A is a diagram illustrating an example multiple AP associationduring station (STA) association;

FIG. 8B is a diagram illustrating an example multiple AP associationprocedure;

FIG. 9 is a diagram illustrating an example multiple AP associationinitiated by STA;

FIG. 10 is a diagram illustrating an example multiple AP service set(SS) element;

FIG. 11 is a diagram illustrating an example multiple AP selectionelement;

FIG. 12 is a diagram illustrating an example of scheduled/random accesscoordinated OFDMA;

FIG. 13 is a signaling diagram illustrating an example of multiple APassociation, cell center/cell edge discovery and data transmission;

FIG. 14 is a diagram illustrating an example guard band for fractionalcoordinated OFDMA;

FIG. 15 is a diagram illustrating an example of downlink-downlink CB/CN;

FIG. 16 is a diagram illustrating an example of uplink-uplink CB/CN;

FIG. 17 is a diagram illustrating an example of uplink-downlink CB/CN;

FIG. 18 is a diagram illustrating an example singling flow forindependent null data packet announcement (NDPA)/null data packet (NDP)and trigger based feedback;

FIG. 19 is a signaling diagram illustrating an example of master triggerbased NDPA/NDP and master trigger based feedback;

FIG. 20 is a signaling diagram illustrating an example of an NDPfeedback request from an AP;

FIG. 21 is a signaling diagram illustrating an example of an NDP triggerfor implicit multiple AP sounding;

FIG. 22 is a signaling diagram illustrating an example of independentNDPA/NDP for reciprocity-based uplink-uplink (UL/UL) CB/CN;

FIG. 23 is a signaling diagram illustrating an example ofmaster-trigger-based NDPA/NDP for UL/UL CB/CN;

FIG. 24 is a signaling diagram illustrating an example of STA-initiatedchannel acquisition;

FIG. 25 is a signaling diagram illustrating an example of AP-initiatedchannel acquisition;

FIG. 26 is a diagram illustrating an example of implicit DL channelacquisition;

FIG. 27 is a diagram illustrating interference in an example scenariofor simultaneous UL and DL traffic;

FIG. 28 is a diagram illustrating example utilization of mesh datatrigger (MDT) and mesh-sounding trigger (MST) frames to CB/CN;

FIG. 29 is a diagram illustrating an example of uplink-uplink CB/CNusing one-sided spatial reuse parameter (SRP) based spatial reuse (SR);

FIG. 30 is a diagram illustrating an example of sparse code multipleaccess (SCMA) gain estimation type 1;

FIG. 31 is a diagram illustrating an example of SCMA gain estimationtype 2;

FIG. 32 is a diagram illustrating an example of uplink-uplink two sidedSRP based SR;

FIG. 33 is a diagram illustrating an example of one-sided DL/UL CB/CNwith a primary UL/DL transmission;

FIG. 34 is a diagram illustrating an example of multiple mastertriggering;

FIG. 35 is a diagram illustrating an example of sequential triggering;

FIG. 36 is a diagram illustrating an example of pre-sounding-basedmaster triggering;

FIG. 37 is a diagram illustrating an example long training field (LTF)construction for AP1 and AP2 for interference alignment (IA);

FIG. 38 is a diagram illustrating an example multiple AP implicitsounding procedure with a sounding frame; and

FIG. 39 is a diagram illustrating an example procedure forself-calibration.

DETAILED DESCRIPTION

FIG. 1A is a diagram illustrating an example communications system 100in which one or more disclosed embodiments may be implemented. Thecommunications system 100 may be a multiple access system that providescontent, such as voice, data, video, messaging, broadcast, etc., tomultiple wireless users. The communications system 100 may enablemultiple wireless users to access such content through the sharing ofsystem resources, including wireless bandwidth. For example, thecommunications systems 100 may employ one or more channel accessmethods, such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tailunique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM(UW-OFDM), resource block-filtered OFDM, filter bank multicarrier(FBMC), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a RAN104/113, a CN 106/115, a public switched telephone network (PSTN) 108,the Internet 110, and other networks 112, though it will be appreciatedthat the disclosed embodiments contemplate any number of WTRUs, basestations, networks, and/or network elements. Each of the WTRUs 102 a,102 b, 102 c, 102 d may be any type of device configured to operateand/or communicate in a wireless environment. By way of example, theWTRUs 102 a, 102 b, 102 c, 102 d, any of which may be referred to as a“station” and/or a “STA”, may be configured to transmit and/or receivewireless signals and may include a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a subscription-based unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watchor other wearable, a head-mounted display (HMD), a vehicle, a drone, amedical device and applications (e.g., remote surgery), an industrialdevice and applications (e.g., a robot and/or other wireless devicesoperating in an industrial and/or an automated processing chaincontexts), a consumer electronics device, a device operating oncommercial and/or industrial wireless networks, and the like. Any of theWTRUs 102 a, 102 b, 102 c and 102 d may be interchangeably referred toas a UE.

The communications systems 100 may also include a base station 114 aand/or a base station 114 b. Each of the base stations 114 a, 114 b maybe any type of device configured to wirelessly interface with at leastone of the WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to oneor more communication networks, such as the CN 106/115, the Internet110, and/or the other networks 112. By way of example, the base stations114 a, 114 b may be a base transceiver station (BTS), a Node-B, an eNodeB, a Home Node B, a Home eNode B, a gNB, a NR NodeB, a site controller,an access point (AP), a wireless router, and the like. While the basestations 114 a, 114 b are each depicted as a single element, it will beappreciated that the base stations 114 a, 114 b may include any numberof interconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 104/113, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals on one or morecarrier frequencies, which may be referred to as a cell (not shown).These frequencies may be in licensed spectrum, unlicensed spectrum, or acombination of licensed and unlicensed spectrum. A cell may providecoverage for a wireless service to a specific geographical area that maybe relatively fixed or that may change over time. The cell may furtherbe divided into cell sectors. For example, the cell associated with thebase station 114 a may be divided into three sectors. Thus, in oneembodiment, the base station 114 a may include three transceivers, i.e.,one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and mayutilize multiple transceivers for each sector of the cell. For example,beamforming may be used to transmit and/or receive signals in desiredspatial directions.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet(UV), visible light, etc.). The air interface 116 may be establishedusing any suitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104/113 and the WTRUs 102 a,102 b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 115/116/117 using wideband CDMA (WCDMA).WCDMA may include communication protocols such as High-Speed PacketAccess (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-SpeedDownlink (DL) Packet Access (HSDPA) and/or High-Speed UL Packet Access(HSUPA).

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement a radio technology such as Evolved UMTS TerrestrialRadio Access (E-UTRA), which may establish the air interface 116 usingLong Term Evolution (LTE) and/or LTE-Advanced (LTE-A) and/orLTE-Advanced Pro (LTE-A Pro).

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement a radio technology such as NR Radio Access, which mayestablish the air interface 116 using New Radio (NR).

In an embodiment, the base station 114 a and the WTRUs 102 a, 102 b, 102c may implement multiple radio access technologies. For example, thebase station 114 a and the WTRUs 102 a, 102 b, 102 c may implement LTEradio access and NR radio access together, for instance using dualconnectivity (DC) principles. Thus, the air interface utilized by WTRUs102 a, 102 b, 102 c may be characterized by multiple types of radioaccess technologies and/or transmissions sent to/from multiple types ofbase stations (e.g., a eNB and a gNB).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.11 (i.e.,Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperabilityfor Microwave Access (WiMAX)), CDMA2000, CDMA20001×, CDMA2000 EV-DO,Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), InterimStandard 856 (IS-856), Global System for Mobile communications (GSM),Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and thelike.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, an industrialfacility, an air corridor (e.g., for use by drones), a roadway, and thelike. In one embodiment, the base station 114 b and the WTRUs 102 c, 102d may implement a radio technology such as IEEE 802.11 to establish awireless local area network (WLAN). In an embodiment, the base station114 b and the WTRUs 102 c, 102 d may implement a radio technology suchas IEEE 802.15 to establish a wireless personal area network (WPAN). Inyet another embodiment, the base station 114 b and the WTRUs 102 c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. Asshown in FIG. 1A, the base station 114 b may have a direct connection tothe Internet 110. Thus, the base station 114 b may not be required toaccess the Internet 110 via the CN 106/115.

The RAN 104/113 may be in communication with the CN 106/115, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (Vol P) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. The data may have varying qualityof service (QoS) requirements, such as differing throughputrequirements, latency requirements, error tolerance requirements,reliability requirements, data throughput requirements, mobilityrequirements, and the like. The CN 106/115 may provide call control,billing services, mobile location-based services, pre-paid calling,Internet connectivity, video distribution, etc., and/or performhigh-level security functions, such as user authentication. Although notshown in FIG. 1A, it will be appreciated that the RAN 104/113 and/or theCN 106/115 may be in direct or indirect communication with other RANsthat employ the same RAT as the RAN 104/113 or a different RAT. Forexample, in addition to being connected to the RAN 104/113, which may beutilizing a NR radio technology, the CN 106/115 may also be incommunication with another RAN (not shown) employing a GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN 106/115 may also serve as a gateway for the WTRUs 102 a, 102 b,102 c, 102 d to access the PSTN 108, the Internet 110, and/or the othernetworks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) and/orthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired and/or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another CN connected to one or more RANs, whichmay employ the same RAT as the RAN 104/113 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities (e.g., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks). For example, the WTRU 102 c shown in FIG. 1A may be configuredto communicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram illustrating an example WTRU 102. As shownin FIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120,a transmit/receive element 122, a speaker/microphone 124, a keypad 126,a display/touchpad 128, non-removable memory 130, removable memory 132,a power source 134, a global positioning system (GPS) chipset 136,and/or other peripherals 138, among others. It will be appreciated thatthe WTRU 102 may include any sub-combination of the foregoing elementswhile remaining consistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In an embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and/or receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

Although the transmit/receive element 122 is depicted in FIG. 1B as asingle element, the WTRU 102 may include any number of transmit/receiveelements 122. More specifically, the WTRU 102 may employ MIMOtechnology. Thus, in one embodiment, the WTRU 102 may include two ormore transmit/receive elements 122 (e.g., multiple antennas) fortransmitting and receiving wireless signals over the air interface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as NR and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs and/or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, a Virtual Reality and/or Augmented Reality (VR/AR) device, anactivity tracker, and the like. The peripherals 138 may include one ormore sensors, the sensors may be one or more of a gyroscope, anaccelerometer, a hall effect sensor, a magnetometer, an orientationsensor, a proximity sensor, a temperature sensor, a time sensor; ageolocation sensor; an altimeter, a light sensor, a touch sensor, amagnetometer, a barometer, a gesture sensor, a biometric sensor, and/ora humidity sensor.

The WTRU 102 may include a full duplex radio for which transmission andreception of some or all of the signals (e.g., associated withparticular subframes for both the UL (e.g., for transmission) anddownlink (e.g., for reception) may be concurrent and/or simultaneous.The full duplex radio may include an interference management unit 139 toreduce and or substantially eliminate self-interference via eitherhardware (e.g., a choke) or signal processing via a processor (e.g., aseparate processor (not shown) or via processor 118). In an embodiment,the WTRU 102 may include a half-duplex radio for which transmission andreception of some or all of the signals (e.g., associated withparticular subframes for either the UL (e.g., for transmission) or thedownlink (e.g., for reception)).

FIG. 10 is a system diagram illustrating the RAN 104 and the CN 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the CN 106.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and/or receive wireless signals from, the WTRU 102a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the UL and/or DL, and the like. As shown in FIG. 10 , the eNode-Bs160 a, 160 b, 160 c may communicate with one another over an X2interface.

The CN 106 shown in FIG. 10 may include a mobility management entity(MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN)gateway (or PGW) 166. While each of the foregoing elements are depictedas part of the CN 106, it will be appreciated that any of these elementsmay be owned and/or operated by an entity other than the CN operator.

The MME 162 may be connected to each of the eNode-Bs 162 a, 162 b, 162 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM and/or WCDMA.

The SGW 164 may be connected to each of the eNode Bs 160 a, 160 b, 160 cin the RAN 104 via the S1 interface. The SGW 164 may generally route andforward user data packets to/from the WTRUs 102 a, 102 b, 102 c. The SGW164 may perform other functions, such as anchoring user planes duringinter-eNode B handovers, triggering paging when DL data is available forthe WTRUs 102 a, 102 b, 102 c, managing and storing contexts of theWTRUs 102 a, 102 b, 102 c, and the like.

The SGW 164 may be connected to the PGW 166, which may provide the WTRUs102 a, 102 b, 102 c with access to packet-switched networks, such as theInternet 110, to facilitate communications between the WTRUs 102 a, 102b, 102 c and IP-enabled devices.

The CN 106 may facilitate communications with other networks. Forexample, the CN 106 may provide the WTRUs 102 a, 102 b, 102 c withaccess to circuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. For example, the CN 106 may include,or may communicate with, an IP gateway (e.g., an IP multimedia subsystem(IMS) server) that serves as an interface between the CN 106 and thePSTN 108. In addition, the CN 106 may provide the WTRUs 102 a, 102 b,102 c with access to the other networks 112, which may include otherwired and/or wireless networks that are owned and/or operated by otherservice providers.

Although the WTRU is described in FIGS. 1A-1D as a wireless terminal, itis contemplated that in certain representative embodiments that such aterminal may use (e.g., temporarily or permanently) wired communicationinterfaces with the communication network.

In representative embodiments, the other network 112 may be a WLAN.

A WLAN in Infrastructure Basic Service Set (BSS) mode may have an AccessPoint (AP) for the BSS and one or more stations (STAs) associated withthe AP. The AP may have an access or an interface to a DistributionSystem (DS) or another type of wired/wireless network that carriestraffic in to and/or out of the BSS. Traffic to STAs that originatesfrom outside the BSS may arrive through the AP and may be delivered tothe STAs. Traffic originating from STAs to destinations outside the BSSmay be sent to the AP to be delivered to respective destinations.Traffic between STAs within the BSS may be sent through the AP, forexample, where the source STA may send traffic to the AP and the AP maydeliver the traffic to the destination STA. The traffic between STAswithin a BSS may be considered and/or referred to as peer-to-peertraffic. The peer-to-peer traffic may be sent between (e.g., directlybetween) the source and destination STAs with a direct link setup (DLS).In certain representative embodiments, the DLS may use an 802.11e DLS oran 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS)mode may not have an AP, and the STAs (e.g., all of the STAs) within orusing the IBSS may communicate directly with each other. The IBSS modeof communication may sometimes be referred to herein as an “ad-hoc” modeof communication.

When using the 802.11ac infrastructure mode of operation or a similarmode of operations, the AP may transmit a beacon on a fixed channel,such as a primary channel. The primary channel may be a fixed width(e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling.The primary channel may be the operating channel of the BSS and may beused by the STAs to establish a connection with the AP. In certainrepresentative embodiments, Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA) may be implemented, for example in in 802.11systems. For CSMA/CA, the STAs (e.g., every STA), including the AP, maysense the primary channel. If the primary channel is sensed/detectedand/or determined to be busy by a particular STA, the particular STA mayback off. One STA (e.g., only one station) may transmit at any giventime in a given BSS.

High Throughput (HT) STAs may use a 40 MHz wide channel forcommunication, for example, via a combination of the primary 20 MHzchannel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHzwide channel.

Very High Throughput (VHT) STAs may support 20 MHz, 40 MHz, 80 MHz,and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz, channels may beformed by combining contiguous 20 MHz channels. A 160 MHz channel may beformed by combining 8 contiguous 20 MHz channels, or by combining twonon-contiguous 80 MHz channels, which may be referred to as an 80+80configuration. For the 80+80 configuration, the data, after channelencoding, may be passed through a segment parser that may divide thedata into two streams. Inverse Fast Fourier Transform (IFFT) processing,and time domain processing, may be done on each stream separately. Thestreams may be mapped on to the two 80 MHz channels, and the data may betransmitted by a transmitting STA. At the receiver of the receiving STA,the above described operation for the 80+80 configuration may bereversed, and the combined data may be sent to the Medium Access Control(MAC).

Sub 1 GHz modes of operation are supported by 802.11af and 802.11ah. Thechannel operating bandwidths, and carriers, are reduced in 802.11af and802.11ah relative to those used in 802.11n, and 802.11ac. 802.11afsupports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space(TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and16 MHz bandwidths using non-TVWS spectrum. According to a representativeembodiment, 802.11ah may support Meter Type Control/Machine-TypeCommunications, such as MTC devices in a macro coverage area. MTCdevices may have certain capabilities, for example, limited capabilitiesincluding support for (e.g., only support for) certain and/or limitedbandwidths. The MTC devices may include a battery with a battery lifeabove a threshold (e.g., to maintain a very long battery life).

WLAN systems, which may support multiple channels, and channelbandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include achannel which may be designated as the primary channel. The primarychannel may have a bandwidth equal to the largest common operatingbandwidth supported by all STAs in the BSS. The bandwidth of the primarychannel may be set and/or limited by a STA, from among all STAs inoperating in a BSS, which supports the smallest bandwidth operatingmode. In the example of 802.11ah, the primary channel may be 1 MHz widefor STAs (e.g., MTC type devices) that support (e.g., only support) a 1MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4MHz, 8 MHz, 16 MHz, and/or other channel bandwidth operating modes.Carrier sensing and/or Network Allocation Vector (NAV) settings maydepend on the status of the primary channel. If the primary channel isbusy, for example, due to a STA (which supports only a 1 MHz operatingmode), transmitting to the AP, the entire available frequency bands maybe considered busy even though a majority of the frequency bands remainsidle and may be available.

In the United States, the available frequency bands, which may be usedby 802.11ah, are from 902 MHz to 928 MHz. In Korea, the availablefrequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the availablefrequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidthavailable for 802.11ah is 6 MHz to 26 MHz depending on the country code.

FIG. 1D is a system diagram illustrating the RAN 113 and the CN 115according to an embodiment. As noted above, the RAN 113 may employ an NRradio technology to communicate with the WTRUs 102 a, 102 b, 102 c overthe air interface 116. The RAN 113 may also be in communication with theCN 115.

The RAN 113 may include gNBs 180 a, 180 b, 180 c, though it will beappreciated that the RAN 113 may include any number of gNBs whileremaining consistent with an embodiment. The gNBs 180 a, 180 b, 180 cmay each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the gNBs 180 a, 180 b, 180 c may implement MIMO technology. For example,gNBs 180 a, 108 b may utilize beamforming to transmit signals to and/orreceive signals from the gNBs 180 a, 180 b, 180 c. Thus, the gNB 180 a,for example, may use multiple antennas to transmit wireless signals to,and/or receive wireless signals from, the WTRU 102 a. In an embodiment,the gNBs 180 a, 180 b, 180 c may implement carrier aggregationtechnology. For example, the gNB 180 a may transmit multiple componentcarriers to the WTRU 102 a (not shown). A subset of these componentcarriers may be on unlicensed spectrum while the remaining componentcarriers may be on licensed spectrum. In an embodiment, the gNBs 180 a,180 b, 180 c may implement Coordinated Multi-Point (CoMP) technology.For example, WTRU 102 a may receive coordinated transmissions from gNB180 a and gNB 180 b (and/or gNB 180 c).

The WTRUs 102 a, 102 b, 102 c may communicate with gNBs 180 a, 180 b,180 c using transmissions associated with a scalable numerology. Forexample, the OFDM symbol spacing and/or OFDM subcarrier spacing may varyfor different transmissions, different cells, and/or different portionsof the wireless transmission spectrum. The WTRUs 102 a, 102 b, 102 c maycommunicate with gNBs 180 a, 180 b, 180 c using subframe or transmissiontime intervals (TTIs) of various or scalable lengths (e.g., containingvarying number of OFDM symbols and/or lasting varying lengths ofabsolute time).

The gNBs 180 a, 180 b, 180 c may be configured to communicate with theWTRUs 102 a, 102 b, 102 c in a standalone configuration and/or anon-standalone configuration. In the standalone configuration, WTRUs 102a, 102 b, 102 c may communicate with gNBs 180 a, 180 b, 180 c withoutalso accessing other RANs (e.g., such as eNode-Bs 160 a, 160 b, 160 c).In the standalone configuration, WTRUs 102 a, 102 b, 102 c may utilizeone or more of gNBs 180 a, 180 b, 180 c as a mobility anchor point. Inthe standalone configuration, WTRUs 102 a, 102 b, 102 c may communicatewith gNBs 180 a, 180 b, 180 c using signals in an unlicensed band. In anon-standalone configuration WTRUs 102 a, 102 b, 102 c may communicatewith/connect to gNBs 180 a, 180 b, 180 c while also communicatingwith/connecting to another RAN such as eNode-Bs 160 a, 160 b, 160 c. Forexample, WTRUs 102 a, 102 b, 102 c may implement DC principles tocommunicate with one or more gNBs 180 a, 180 b, 180 c and one or moreeNode-Bs 160 a, 160 b, 160 c substantially simultaneously. In thenon-standalone configuration, eNode-Bs 160 a, 160 b, 160 c may serve asa mobility anchor for WTRUs 102 a, 102 b, 102 c and gNBs 180 a, 180 b,180 c may provide additional coverage and/or throughput for servicingWTRUs 102 a, 102 b, 102 c.

Each of the gNBs 180 a, 180 b, 180 c may be associated with a particularcell (not shown) and may be configured to handle radio resourcemanagement decisions, handover decisions, scheduling of users in the ULand/or DL, support of network slicing, dual connectivity, interworkingbetween NR and E-UTRA, routing of user plane data towards User PlaneFunction (UPF) 184 a, 184 b, routing of control plane informationtowards Access and Mobility Management Function (AMF) 182 a, 182 b andthe like. As shown in FIG. 1D, the gNBs 180 a, 180 b, 180 c maycommunicate with one another over an Xn interface.

The CN 115 shown in FIG. 1D may include at least one AMF 182 a, 182 b,at least one UPF 184 a,184 b, at least one Session Management Function(SMF) 183 a, 183 b, and possibly a Data Network (DN) 185 a, 185 b. Whileeach of the foregoing elements are depicted as part of the CN 115, itwill be appreciated that any of these elements may be owned and/oroperated by an entity other than the CN operator.

The AMF 182 a, 182 b may be connected to one or more of the gNBs 180 a,180 b, 180 c in the RAN 113 via an N2 interface and may serve as acontrol node. For example, the AMF 182 a, 182 b may be responsible forauthenticating users of the WTRUs 102 a, 102 b, 102 c, support fornetwork slicing (e.g., handling of different PDU sessions with differentrequirements), selecting a particular SMF 183 a, 183 b, management ofthe registration area, termination of NAS signaling, mobilitymanagement, and the like. Network slicing may be used by the AMF 182 a,182 b in order to customize CN support for WTRUs 102 a, 102 b, 102 cbased on the types of services being utilized WTRUs 102 a, 102 b, 102 c.For example, different network slices may be established for differentuse cases such as services relying on ultra-reliable low latency (URLLC)access, services relying on enhanced massive mobile broadband (eMBB)access, services for machine type communication (MTC) access, and/or thelike. The AMF 162 may provide a control plane function for switchingbetween the RAN 113 and other RANs (not shown) that employ other radiotechnologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP accesstechnologies such as WiFi.

The SMF 183 a, 183 b may be connected to an AMF 182 a, 182 b in the CN115 via an N11 interface. The SMF 183 a, 183 b may also be connected toa UPF 184 a, 184 b in the CN 115 via an N4 interface. The SMF 183 a, 183b may select and control the UPF 184 a, 184 b and configure the routingof traffic through the UPF 184 a, 184 b. The SMF 183 a, 183 b mayperform other functions, such as managing and allocating UE IP address,managing PDU sessions, controlling policy enforcement and QoS, providingdownlink data notifications, and the like. A PDU session type may beIP-based, non-IP based, Ethernet-based, and the like.

The UPF 184 a, 184 b may be connected to one or more of the gNBs 180 a,180 b, 180 c in the RAN 113 via an N3 interface, which may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between the WTRUs 102a, 102 b, 102 c and IP-enabled devices. The UPF 184, 184 b may performother functions, such as routing and forwarding packets, enforcing userplane policies, supporting multi-homed PDU sessions, handling user planeQoS, buffering downlink packets, providing mobility anchoring, and thelike.

The CN 115 may facilitate communications with other networks. Forexample, the CN 115 may include, or may communicate with, an IP gateway(e.g., an IP multimedia subsystem (IMS) server) that serves as aninterface between the CN 115 and the PSTN 108. In addition, the CN 115may provide the WTRUs 102 a, 102 b, 102 c with access to the othernetworks 112, which may include other wired and/or wireless networksthat are owned and/or operated by other service providers. In oneembodiment, the WTRUs 102 a, 102 b, 102 c may be connected to a localData Network (DN) 185 a, 185 b through the UPF 184 a, 184 b via the N3interface to the UPF 184 a, 184 b and an N6 interface between the UPF184 a, 184 b and the DN 185 a, 185 b.

In view of FIGS. 1A-1D, and the corresponding description of FIGS.1A-1D, one or more, or all, of the functions described herein withregard to one or more of: WTRU 102 a-d, Base Station 114 a-b, eNode-B160 a-c, MME 162, SGW 164, PGW 166, gNB 180 a-c, AMF 182 a-ab, UPF 184a-b, SMF 183 a-b, DN 185 a-b, and/or any other device(s) describedherein, may be performed by one or more emulation devices (not shown).The emulation devices may be one or more devices configured to emulateone or more, or all, of the functions described herein. For example, theemulation devices may be used to test other devices and/or to simulatenetwork and/or WTRU functions.

The emulation devices may be designed to implement one or more tests ofother devices in a lab environment and/or in an operator networkenvironment. For example, the one or more emulation devices may performthe one or more, or all, functions while being fully or partiallyimplemented and/or deployed as part of a wired and/or wirelesscommunication network in order to test other devices within thecommunication network. The one or more emulation devices may perform theone or more, or all, functions while being temporarilyimplemented/deployed as part of a wired and/or wireless communicationnetwork. The emulation device may be directly coupled to another devicefor purposes of testing and/or may performing testing using over-the-airwireless communications.

The one or more emulation devices may perform the one or more, includingall, functions while not being implemented/deployed as part of a wiredand/or wireless communication network. For example, the emulationdevices may be utilized in a testing scenario in a testing laboratoryand/or a non-deployed (e.g., testing) wired and/or wirelesscommunication network in order to implement testing of one or morecomponents. The one or more emulation devices may be test equipment.Direct RF coupling and/or wireless communications via RF circuitry(e.g., which may include one or more antennas) may be used by theemulation devices to transmit and/or receive data.

In IEEE 802.11ac, very high throughput (VHT) STAs may support 20 MHz, 40MHz, 80 MHz, and 160 MHz wide channels. The 40 MHz and 80 MHz channelsmay be formed by combining contiguous 20 MHz channels, similar to IEEE802.11n. A 160 MHz channel may be formed either by combining 8contiguous 20 MHz channels or by combining two non-contiguous 80 MHzchannels. This may be referred to as an 80+80 configuration. For the80+80 configuration, the data, after channel encoding, may be passedthrough a segment parser that divides it into two streams. Inverse fastFourier transform (IFFT) and time domain processing may be performed oneach stream separately. The streams may then be mapped onto the twochannels and the data transmitted. At the receiver, this mechanism maybe reversed, and the combined data may be sent to the MAC.

IEEE 802.11af and 802.11ah support sub 1 GHz modes of operation. Forthese specifications, the channel operating bandwidths and carriers maybe reduced relative to those used in IEEE 802.11n and 802.11ac. IEEE802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV WhiteSpace (TVWS) spectrum, and IEEE 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8MHz, and 16 MHz bandwidths using non-TVWS spectrum. For IEEE 802.11ah,this may be used to support for meter type control (MTC) devices in amacro coverage area. MTC devices may have limited capabilities,including only supporting limited bandwidths, but may also have arequirement for a very long battery life.

WLAN systems that support multiple channels and channel widths, such asIEEE 802.11n, 802.11ac, 802.11af, and 802.11ah, may include a channeldesignated as the primary channel. The primary channel may have abandwidth equal to the largest common operating bandwidth supported byall STAs in the BSS. The bandwidth of the primary channel may,therefore, be limited by the STA, of all STAs operating in a BSS, whichsupports the smallest bandwidth operating mode. For IEEE 802.11ah, forexample, the primary channel may be 1 MHz wide if there are STAs (e.g.,MTC devices) that only support a 1 MHz mode even if the AP, and otherSTAs in the BSS, supports a 2 MHz, 4 MHz, 8 MHz, 16 MHz, or otherchannel bandwidth operating mode. All carrier sensing and NAV settingsmay depend on the status of the primary channel. For example, if theprimary channel is busy, for example, due to a STA supporting only a 1MHz operating mode transmitting to the AP, then the entire availablefrequency band may be considered busy even though the majority of itremains idle and available.

In the United States, the available frequency bands that may be used byIEEE 802.11ah may be from 902 MHz to 928 MHz. In Korea, the availablefrequency bands may be from 917.5 MHz to 923.5 MHz, and in Japan, theavailable frequency bands may be from 916.5 MHz to 927.5 MHz. The totalbandwidth available for IEEE 802.11ah may be 6 MHz to 26 MHz, dependingon the country code.

The IEEE 802.11™ High Efficiency WLAN (HEW) includes embodiments toenhance the quality of service all users experience for a broad spectrumof wireless users in many scenarios, including high-density scenarios inthe 2.4 GHz, 5 GHz and 6 GHz bands. New use cases that support densedeployments of AP, STAs, and associated Radio Resource Management (RRM)technologies are being considered by the 802.11 HEW.

Potential applications for HEW include emerging usage scenarios, such asdata delivery for stadium events, high user density scenarios, such astrain stations or enterprise/retail environments, and increaseddependence on video delivery and wireless services for medicalapplications.

In 802.11ax or HEW, the measured traffic for a variety of applicationshas a large likelihood for short packets, and there are networkapplications that may also generate short packets. The applications mayinclude virtual office, transmit power control (TPC) acknowledgement(ACK), video streaming ACK, device/controller (such as mice, keyboardsand game controls), access (e.g., probe request/response), networkselection (e.g., probe requests and access network query protocol(ANQP)) and network management (e.g., control frames). Further,multi-user (MU) features that include uplink (UL) and downlink (DL)OFDMA and UL and DL MU-MIMO have been introduced, and a mechanism formultiplexing UL random access for different purposes has been specified.

The IEEE 802.11 Extremely High Throughput (EHT) includes embodiments tofurther increase peak throughput and improve efficiency of the IEEE802.11 networks. The use cases and applications for EHT may include highthroughput and low latency applications, such as video-over-WLAN,augmented reality (AR) and virtual reality (VR). A list of features inthe EHT may include multiple AP, multi-band, 320 MHz bandwidth, 16spatial streams, HARQ, full duplex (in time and frequency domains), APcoordination, semi-orthogonal multiple access (SOMA), and new designsfor 6 GHz channel access.

In a typical IEEE 802.11 network, STAs may be associated with a singleAP and may transmit to and from that AP with little or no coordinationwith transmissions in neighboring BSSs. A STA may defer to anoverlapping basic service set (OBSS) transmission based on a CSMAprotocol that is entirely independent between BSSs. In IEEE 802.11ax,some level of coordination between OBSSs was introduced by spatialre-use (SR) procedures and may allow OBSS transmissions based on anadjusted energy detection threshold (e.g., using the OBSS PD procedure)or by knowledge of the amount of interference that may be tolerated by areceiving OBSS STA (e.g., using the SRP procedure).

Embodiments described herein may provide for procedures that enable morecoordination between the OBSSs by allowing transmission to or frommultiple APs to one or more STAs. The multiple AP coordination betweenOBSSs may be performed within an unlicensed band and/or specific to anIEEE 802.11 protocol.

Multiple AP/eNBs may transmit to the same or multiple STAs/WTRUs in thesame or different time and frequency resource using jointprocessing/transmission, with the objective of improving the overallthroughput for the considered STA/WTRU. Dynamic cell selection may betreated as a special case of joint processing in which only one of theset of AP/eNBs is actively transmitting data at any time. On the otherhand, multiple AP/eNBs may transmit to different STAs/WTRUs (e.g., eachAP/eNB serving its own STA/WTRU) in the same or different time andfrequency resource using coordinated beamforming/scheduling, with theobjective of reducing interference experienced by each STA/WTRU.Significant improvements in cell average and/or cell edge throughput maybe achieved by multiple AP/eNB coordination. Multiple transmit antennasmay be assumed to be available for each STA/WTRU/AP/base station.Simultaneous interference suppression for other STAs/WTRUs and signalquality optimization for the desired STA/WTRU may be handled throughspatial domain signal processing at each base station.

In general, some degree of channel state information may be assumed tobe available at the APs or base stations, through, for example, explicitfeedback. Also, a certain degree of timing/frequency synchronization maybe assumed, such that more complicated signal processing to deal withinter-carrier or inter-symbol interference may be avoided.

Multiple AP transmission schemes in WLANs may be classified based oncoordinated OFDMA, coordinated nulling/beamforming, and coordinatedSU/MU transmission. For coordinated SU transmission, multiple APs maytransmit to a STA in one resource unit (RU). Coordinated SU transmissionmay be one of the following (in order of increased complexity): dynamicselection, coordinated SU beamforming and coordinated MU beamforming.For coordinated point selection, the transmission may be dynamicallyselected from one of the set of APs and may include HARQ. Forcoordinated SU beamforming, the transmission may be from the multipleAPs simultaneously, and the transmission may be beamformed. Forcoordinated MU beamforming, multiple APs may transmit or receive datato/from multiple STAs in one RU.

FIG. 2 illustrates an example 200 of coordinated orthogonalfrequency-division multiple access (OFDMA), which may be used incombination of any of other embodiments described herein. In coordinatedOFDMA, each group of RUs may be used by one AP (e.g., 214 a, 214 b, 214c, or 214 d) to transmit or receive data. For example, as illustrated inFIG. 2 , the STAs 202 a-2021 may be divided to two groups, cell centerSTAs 202 a, 202 d, 202 g, 202 j, and cell edge STAs 202 b, 202 c, 202 e,202 f, 202 h, 202 i, 202 k, 202 j. The APs 214 a, 214 b, 214 c, 214 dmay allow its STAs 202 a, 202 d, 202 g, 202 j (i.e. cell center STAs)that are not affected by interference to use the entire bandwidth.However, the APs 214 a, 214 b, 214 c, 214 d may limit its STAs 202 b,202 c, 202 e, 202 f, 202 h, 202 i, 202 k, 2021 (i.e. cell edge STAs)that may be affected by interference to use only partial frequencybandwidth. For example, the STA 202 a is allowed to use the entirebandwidth (e.g., full spectrum/channel) while the STAs 202 b, 202 c arelimited to use only certain part of the bandwidth. The data orinformation communicated between the APs 214 a, 214 b, 214 c, 214 d andthe STAs 202 a-2021 may be beamformed or have MU-MIMO on each RU 205,210, 220, 225, 230, 235, 240, 245. Complexity may be relatively low tomedium. In one embodiment, the APs may split the OFDMA resource units(RUs) between themselves in a coordinated manner, with each APrestricted to specific RUs. In another embodiment, the APs may allowSTAs that are not affected by interference, or will not affect others,to use the entire bandwidth while restricting access for the STAs thatmay be affected. This is called fractional frequency reuse (FFR).

FIG. 3 illustrates an example resource allocation 300 for coordinatedOFDMA, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 3 , STAs (e.g., cell centerSTAs) associated with group1 resources 305, 315 (e.g., center group RUs)may be allowed to use the entire band (e.g., subband1 and subband2),STAs (e.g., cell edge STAs) associated with the group2 resource 310 orgroup3 resource 320 may be limited to use only allocated resource (e.g.,subband1 or subband 2).

FIG. 4 illustrates an example 400 of coordinated beamforming/coordinatednulling (CB/CN), which may be used in combination of any of otherembodiments described herein. In coordinated beamforming/coordinatednulling, each AP (e.g., AP1 414 a and AP2 414 b) may apply precoding totransmit information to or from its desired STA or STAs (e.g., STA1 402a and STA2 402 b) and suppress interference to or from it. In theexample illustrated in FIG. 4 , the data for each STA (e.g., STA1 402 aor STA2 402 b) may only be needed at its associated AP (e.g., AP1 414 aor AP2 414 b), although channel information from the other STA (e.g.,STA2 402 b or STA1 402 a) may be needed at both APs (e.g., AP1 414 a andAP2 414 b).

FIG. 5 illustrates an example 500 of coordinated nulling/coordinatedbeamforming (CB/CN) using interference alignment (IA), which may be usedin combination of any of other embodiments described herein. Ininterference alignment, APs may precode the information for STAs suchthat the undesired information (e.g., STA1 information is undesired forSTA2) falls into an interference subspace at STAs after the APs' signalspass through the channel. In the example illustrated in FIG. 5 where twoAPs, AP1 514 a and AP2 514 b, and two STAs, STA A 502 a and STA B 502 b,are in a wireless medium, AP1 514 a and AP2 514 b may be in the same BSSand connected through a central unit that distributes the informationfor STA A 502 a, for example a₁∈

^(1/3M×1) and a₂∈

^(1/3M×1) and STA B 502 b, for example b₁∈

^(1/3M×1) and b₂∈

^(1/3M×1), to the AP1 514 a and AP2 514 b, where M may be the number ofantennas at STAs 502 a, 502 b and APs 514 a, 514 b. The informationavailable at AP1 514 a may be a₁ and b₁. The information available atAP2 514 b may be a₂ and b₂. The information exchange between APs 514 a,514 b through the central unit may be slow or assumed to be none.However, the APs 514 a, 514 b may communicate between them through awireless medium with low-data rate but reliable communication protocols.The channels between AP1 514 a and STA A 502 a, STA B 502 b may bedenoted by H₁₁, H₂₁∈

^(M×M), and the channels between AP2 514 b and STA A 502 a, STA B 502 bmay be denoted by H₁₂, H₂₂∈

^(M×M).

The operations at AP1 514 a and AP2 514 b for a group of subcarriers ora single subcarrier may be as follows:t ₁ =H ₁₁ ⁻¹ V ₁ b ₁ +H ₂₁ ⁻¹ V ₂ a ₁t ₂ =H ₁₂ ⁻¹ V ₁ b ₂ +H ₂₂ ⁻ V ₂ a ₂,where t₁∈

^(M×1) and t₂∈

^(M×1) may be the transmitted symbols from AP1 514 a and AP2 514 b,respectively, and V₁ and V₂ may be the interference subspaces for STA A502 a and STA B 502 b, respectively. The received symbols at the STA A502 a and STA B 502 b may be shown as:

$r_{1} = {\underset{\underset{Alignment}{Interference}}{\underset{︸}{\begin{matrix}V_{1} & \left( {b_{1} + b_{2}} \right)\end{matrix}}} + {H_{12}H_{22}^{- 1}V_{2}a_{2}} + {H_{11}H_{21}^{- 1}V_{2}a_{1}} + n_{1}}$$r_{2} = {\underset{\underset{Alignment}{Interference}}{\underset{︸}{\begin{matrix}V_{2} & \left( {a_{1} + a_{2}} \right)\end{matrix}}} + {H_{22}H_{12}^{- 1}V_{1}b_{2}} + {H_{21}H_{11}^{- 1}V_{1}} + n_{2}}$

Because of the precoding at AP1 514 a and AP2 514 b, the interferencecomponents, due to cross channels, may fall in the same subspace, forexample V₁ for STA A 502 a and V₂ for STA B 502 a. This scheme maycorrespond to a particular case of an interference alignment (IA)scheme. The main benefit for this particular scheme may be that the AP1514 a or AP2 514 b may not need to use the channel state informationrelated to AP2 514 b or AP1 514 a. Hence, it may decrease the traffic byeliminating the need for information exchange between the APs 514 a, 514b. In addition, it may serve 4/3M information by using APs 514 a, 514 band STAs 502 a, 502 b equipped with M antennas.

In coordinated single user (SU) or multi user (MU) transmission,multiple APs may coordinate to simultaneously transmit information to orfrom a single STA or multiple STAs. In this case, both the channelinformation and the data for the STAs may be needed at both APs. Thecoordinated SU or MU transmission may be, for example, one ofcoordinated SU transmission or coordinated MU beamforming.

For coordinated SU transmission, multiple APs may transmit to a STA inone RU and may be one of (in order of increased complexity) dynamicpoint selection, coordinated SU beamforming or joint precoding. Fordynamic point selection, the transmission may be dynamically selectedfrom one of the set of APs and may incorporate HARQ.

FIG. 6 illustrates an example 600 of single user (SU) joint precodedmultiple AP transmission or coordinated SU beamforming, which may beused in combination of any of other embodiments described herein. Incoordinated joint precoding, the transmission may be simultaneously fromthe multiple APs (e.g., AP1 614 a and AP2 614 b), and the transmissionmay be beamformed or precoded to the desired STA (e.g., STA1 602 a) onone or more RUs. For example, as illustrated in FIG. 6 , AP1 614 a andAP2 614 b may send signals to STA1 602 in one UR for the coordinated SUtransmission.

FIG. 7 illustrates an example 700 of multi user (MU) precoded multipleAP transmission or coordinated MU beamforming, which may be used incombination of any of other embodiments described herein. Forcoordinated MU beamforming, multiple APs (e.g., AP1 714 a and AP2 714 b)may transmit or receive data to/from multiple STAs (e.g., STA1 702 a andSTA2 702 b) on one or more RUs. For example, as illustrated in FIG. 7 ,AP1 714 a and AP2 714 b coordinate (e.g., via backhaul) tosimultaneously transmit/receive data to/from STA1 702 a and STA2 702 bin one or more RUs. Multiple AP schemes described herein may includescenarios related to coordinated beamforming and joint processing.

In IEEE 802.11 systems, a STA may send an association request to an AP,and if the association is successful, receive an association responsefrom the AP to indicate that it is a member of the BSS. For multiple APsystems, an AP may be affected by multiple APs and may require somelevel of association with each AP. Multiple AP association describedherein may enable a single STA to discover multiple APs and associatewith more than one AP.

Further, to enable coordinated OFDMA in trigger based IEEE 802.11systems, such as IEEE 802.11ax and beyond, embodiments described hereinmay enable STAs to identify whether the STAs are cell center or celledge STAs and to feedback this information to the AP in a trigger-basedOFDMA system. Embodiments described herein may also enable the STAsand/or APs to perform trigger-based scheduled coordinated OFDMA schemesand/or trigger-based random access coordinated OFDMA schemes. The OFDMAtransmissions from the different BSSs may be synchronized to ensureorthogonality in the presence of different timing offsets.

Further, for coordinated beamforming and coordinated nulling, thetransmitter (or transmitting STA) may estimate the effective channels toboth the desired receiver (or desired receiving STA) and the interfereereceiver (e.g., the receiver or STA subject to interference from thetransmitter). Channel feedback may be used to feedback from the desiredreceiver that is within the BSS. The feedback may also be requested fromthe receiver in another BSS or a BSS associated to the current BSS usingmultiple AP association. Further, embodiments described herein mayenable requesting feedback in an efficient manner for both the desiredand interferee receiver. The direction of the desired transmission(e.g., uplink or downlink) and the interferee (e.g., uplink or downlink)may be considered. Both trigger-based and non-trigger-based proceduresmay be provided for.

Further, embodiments described herein may provide for design specifictransmission procedures for the different system architectures withrespect to obtaining an effective channel and designing effectiveprecoders. The architectures may be based on whether: (1) bothtransmitters are DL from APs (DL-DL); (2) both transmitters are uplink(UL-UL) from STAs; or (3) one of the transmitters is an AP and the othera STA or vice versa (DL-U or UL-DL). In one example, for UL-ULarchitectures, spatial reuse parameter (SRP)-based spatial reuse (SR) inIEEE 802.11ax may be used or modified. In SRP-based spatial reuse (SR),a STA may receive an SRP PPDU with an indication of the maximum amountof interference that the AP may tolerate from another STA in aneighboring BSS that wants to simultaneously transmit while the AP isreceiving a frame from a specific STA (e.g., in an SR manner).

Further, to enable multiple AP transmission in the DL with beamformingor beam nulling techniques, APs may need to know the DL channel stateinformation (CSI) for all STAs. Assuming that DL and UL channels arereciprocal, the APs may obtain the DL CSI from reception of a ULreference, pilot or training signal transmitted from the STAs. Fromthis, the APs may obtain information such as path losses from differentSTAs to different APs, which may assist the APs in achieving multiple APDL beamforming or nulling. However, if the UL transmissions from theSTAs are power-controlled, signals received from all the STAs may havethe same or similar power levels. Accordingly, in such scenarios, the APmay not be able to determine the path losses and pathloss informationbetween APs and STAs may, therefore, be obtained. If the STA ispower-limited, the reciprocal channel estimate at the AP derived fromthe STA transmitting an NDP may be poor due to it potentially beingnoise-limited. In such scenarios, the channel estimate to enable DLSU-MIMO or MU-MIMO may be performed and improved.

The AP association procedure may occur as part of the typical STAassociation procedure. FIG. 8A illustrates an example multiple APassociation 800 during STA association, which may be used in combinationof any of other embodiments described herein.

In the example illustrated in FIG. 8A, the STA 802 sends probe requestframes 805 a, 805 b (and/or authentication request frames 815 a, 815 b)and may identify the candidate APs such as AP1 814 a and AP2 814 b. Inembodiments, each of the probe request frames 805 a, 805 b may include,but is not limited to, a request for multiple AP association,transmission, and/or reception capabilities. The APs (e.g., AP1 814 aand AP2 814 b) that received the probe request frames 805 a, 805 b(and/or authentication request frames 815 a, 815 b) send probe responseframes 810 a, 810 b (and/or authentication response frames 820 a, 820 b)to the STA 802. Each of the probe response frames 810 a, 810 b mayinclude, but is not limited to, multiple AP association, transmission,and/or reception capabilities. It may also include candidatecoordinating APs (e.g., AP1 814 a and AP2 814 b) and their multiple APcapabilities (e.g., fractional frequency reuse (FFR), coordination, orjoint transmission).

A STA 802 may connect to a primary AP (e.g., AP1 814 a). In embodiments,the primary AP may be defined as the AP to which the STA would otherwiseconnect to for a single AP scenario. This may be, for example, the APthat the STA would otherwise connect to for IEEE 802.11 transmissions(e.g., IEEE 802.11ax or earlier). The secondary APs (e.g., AP2 814 b)may be additional APs used for multiple AP transmission. In embodiments,the primary AP needs to be part of the transmission. In otherembodiments, the best AP of the multiple AP service set may be used fortransmission. There may be more than one secondary AP in the multiple APservice set, and the APs may be ordered, for example, as primary AP,secondary 1 AP, secondary 2 AP, tertiary AP, etc. The multiple APservice set or multiple AP service set may comprise a plurality of APsthat are able to support the multiple AP association, transmission,and/or reception between the STA and the multiple APs.

As illustrated in FIG. 8A, the STA 802 may send one or more multiple APassociation request frames 825 to the APs 814 a, 814 b with anindication of the priority in which the APs 814 a, 814 b are to beassociated (e.g., primary AP, secondary AP, tertiary AP or AP1, AP2).The AP priority order may be explicitly signaled in the multiple APassociation request frame 825 or may be implicitly signaled by the orderin which the AP identifiers appear in the multiple AP associationrequest frame 825.

The STA may identify the priority order from the strength at whichbeacons or probe response frames 810 a, 810 b are received from each ofthe APs. The beacons or probe response frames 810 a, 810 b may includethe APs' capability information regarding multiple APtransmission/reception, such as a multiple AP service set elementdescribed in FIG. 10 as an example. The APs 814 a, 814 b may inform theSTA 802 of the possible multiple AP combinations (e.g., a multiple APservice set) and associated multiple AP capabilities, and the STAs mayselect the subset to be used for the multiple AP association requestframe 825.

The multiple AP association request frame 825 may indicate the type ortypes of coordination requested. In one example, the STA 802 may requesta specific coordination type. In some embodiments, the STA 802 mayrequest all the coordination types that it is able to support. Examplesof the coordination types may include, but are not limited to,coordinated beamforming, coordinated OFDMA, joint transmission, andmultiple AP HARQ. On receipt of the multiple AP association requestframe 825, the APs 814 a, 814 b may perform some AP coordinationprocedures 830 to ensure that they are able to coordinate in the mannerrequested. This may involve higher layer signaling through a backhaul oran AP coordinator. Alternatively or additionally, the primary AP (e.g.,AP1 814 a) may send an over the air (OTA) signal to the secondary AP(e.g., AP2 814 b) with details of the coordination request and type ofdata needed. The multiple AP association request 825 may be sent by theSTA 802 to add, remove or change the APs 814 a, 814 b which the STA 802is associated with, such as in the case of blockage of an AP in thepreviously requested multiple AP service set. As an example, themultiple AP association request frame 825 may include a multiple APselection element as illustrated in FIG. 11 . The multiple APassociation request frame 825 may be broadcasted to all the APs 814 a,814 b in the multiple AP service set or transmitted to the individualAPs 814 a, 814 b separately.

The APs 814 a, 814 b may then send multiple AP association responseframes 835 a, 835 b to the STA 802. In embodiments, each AP 814 a, 814 bmay send an independent multiple AP association response frame 835 a,835 b to the STA 802. The multiple AP association response frame 835 a,835 b may be sent in a manner that ensures separability in the code,time, frequency and/or space domains. Alternatively or additionally, themultiple AP association response frame 835 a, 835 b may be sent usingthe DL multiple AP scheme requested, such as joint transmission, as atest of the system. The multiple AP association response frame 835 a,835 b may accept the multiple AP scheme requested by the STA 802 (e.g.,by the multiple AP association request frame 825). The multiple APresponse frame 835 a, 835 b may reject the multiple AP scheme requestedby the STA 802 (e.g., by the multiple AP association request frame 825).The multiple AP association response frame 835 a, 835 b may suggest analternative or additional scheme to the scheme requested by the STA.

The STA 802 may then reply with a multiple AP associationacknowledgement (ACK) frame 840 a, 840 b to both APs 814 a, 814 b toensure that both APs 814 a, 814 b know that the STA 802 is now ready forthe multiple AP transmission/reception setup. On a condition that one ofthe APs 814 a, 814 b is unable to accept the multiple AP associationrequested by the STA 802 and does not send a multiple AP associationresponse frame 835 a, 835 b, the multiple AP ACK frame 840 a, 840 b mayensure that the other AP (e.g., AP1 814 a or AP2 814 b) is aware that itis the primary AP and should not set up a multiple APtransmission/reception procedures. For example, in case that AP2 814 bdoes not accept the multiple AP association request frame 825 requestedby the STA 802 and does not send the multiple AP association responseframe 835 b, the STA 802 may transmit the multiple AP association ACKframe 840 a to AP1 814 a to ensure that AP1 814 a is the primary AP thatis not going to set up the multiple AP transmission/receptionprocedures. Once the STA 802 receives the multiple AP association ACKframes 840 a, 840 b from the APs 814 a, 814 b, the STA 802 may initiatemultiple AP transmission/reception scheme with the APs 814 a, 814 b andperform data transmission 845 with the APs 814 a, 814 b.

Assuming that AP1 814 a and AP2 814 b are in the same multiple APservice set, packets may be transmitted from the APs 814 a, 814 b in themultiple AP service set such that they do not overlap at the STA 802.For example, AP1 814 a and AP2 814 b may send probe response frames 810a, 810 b such that they do not overlap and such that the APIs proberesponse frame 810 a has time to be decoded before arrival of the AP2'sprobe response frame 810 b. This may also be applicable to the multipleAP association response. For example, AP1 814 a and AP2 814 b may sendmultiple AP association response frames 835 a, 835 b such that they donot overlap and such that the APIs multiple AP association responseframe 835 a has time to be decoded before arrival of the AP2's multipleAP association response frame 835 b. In other words, the APs 814 a, 814b may send packets (e.g., probe response frames 810 a, 810 b or multipleAP association response frames 835 a, 835 b) to the STA 802 based on apredetermined order or random order such that the packets do not overlapeach other at the STA 802. The order may be determined by the APs 814 a,814 b, the STA 802, a network operator, or a network controller.

FIG. 8B illustrates an example multiple AP association procedure 850,which may be used in combination of any of other embodiments describedherein. At step 855, a STA may transmit one or more probe request framesto multiple APs in its proximity to indicate that the STA is able tosupport multiple AP operation such as transmission and/or reception withthe multiple APs. Before sending the probe request frames, the STA mayselect the multiple APs based on active scanning. For example, if theSTA has no information about APs around the STA, the STA may broadcastthe probe request frames to all the neighbor APs. If the STA has theinformation about the network operators or network carrier for which theAPs support, the STA may select specific APs with the service setidentifiers (SSIDs) that correspond to the network operator or networkcarrier. The STA may then transmit probe request frames to the specificAPs to elicit probe response frames from the selected APs. If the STAhas the information of particular APs' addresses (e.g., BSSIDs), the STAmay select those APs to send probe request frames and receive proberesponse frames from those APs. The probe request frame may include oneor more indicators indicating that the STA is able to support themultiple AP operation with the multiple APs. The probe request frame mayalso include one or more indicators requesting the AP whether the APreceived the probe request frame are part of a multiple AP service setthat provides the STA the multiple AP operation.

At step 860, the STA may receive, from the multiple APs, probe responseframes in response to the probe request frame(s). Each of the proberesponse frames may include one or more indicators indicating multipleAP operation capabilities of the APs that transmitted the probe responseframes to the STA. For example, each of the probe response framesincludes a multiple AP service set element, as illustrated in FIG. 10 ,for each of the APs that transmitted the probe response frame. Based onthe multiple AP service set element, the STA may identify multiple APparameters (e.g., group and multiple AP service set) for the multiple APoperation with the multiple APs. The multiple AP service set element mayinclude, but are not limited to, a multiple AP joint transmissioncapability, a multiple AP hybrid automatic repeat request (HARQ)capability, a multiple AP multiple-input multiple-output (MIMO)capability, a dynamic AP selection capability, a multiple AP roamingcapability, and a multiple AP coordinated beamforming capability.

In one embodiments, if AP1, AP2 and AP3 belong to the same multiple APservice set that provide the multiple AP operation to the STA, each ofthe probe response frames provides capability information for each ofAP1, AP2, and AP3. For example, the probe response frame transmitted byAP1 includes capability information of AP2 and AP3 in addition to thecapability information of transmitting AP1. Similarly, the proberesponse frame transmitted by AP2 includes capability information of AP1and AP3 in addition to the capability information of transmitting AP2.

In another embodiment, if AP1 and AP2 belong to the same multiple APservice set, but AP3 does not belong to the multiple AP service set towhich AP1 and AP2 belong, each of the probe response frames transmittedfrom AP1 and AP2 includes capability information of each of AP1 and AP2.However, the probe response frame transmitted from AP3 may not includecapability information for AP1 and AP2, but may include capabilityinformation of other APs in a different multiple AP service set to whichAP3 belongs. For example, the probe response frame transmitted by AP1includes capability information of AP2 in addition to the capabilityinformation of AP1. However, the probe response frame transmitted by AP3may include capability information of AP3, AP4 and AP5 where AP3, AP4,and AP5 form a different multiple AP service set than the multiple APservice set to which AP1 and AP2 belong.

At step 865, the STA may transmit authentication request frames to themultiple APs and receive, at step 870, authentication response framesfrom the multiple APs. In one example, as illustrated in FIG. 8A, theSTA may transmit an authentication request frame 815 a to AP1 814 a andreceive an authentication response frame 820 a from AP1 814 a. The STAmay then transmit another authentication request frame 815 b to AP2 814b and receive another authentication response frame 820 b from AP2 814b. In another example, as illustrated in FIG. 9 , the STA may onlytransmit an authentication request frame 915 to AP1 914 a and receive anauthentication response frame 920 from AP1 914 a in case that the STA isassociated with AP1 914 a before the multiple AP association procedureis initiated with AP2 914 b.

At step 875, the STA may transmit one or more multiple AP associationrequest frames to the multiple APs for the multiple AP association.Specifically, the multiple AP association request frame may enable themultiple APs to coordinate each other to form the multiple APassociation that provides the multiple AP operation to the STA. Forexample, once the APs receive the multiple AP association request frame,the APs may communicate each other APs via the backhaul link between theAPs until all the APs in the multiple AP service set become aware of theSTA's association with the APs in the multiple AP service set. In anexample, a primary AP may send OTA signals to secondary APs (andtertiary APs) to inform that the STA is associated with the multiple APservice set that includes the APs (e.g., the primary, secondary, andtertiary APs) for the multiple AP operation. The multiple AP associationrequest frame may be broadcasted to all the APs in the multiple APservice set or individually transmitted to each of the multiple APs inthe multiple AP service set.

At step 880, the STA may receive, from the multiple APs, multiple APassociation response frames that includes one or more indicatorsindicating acceptance or rejection of the multiple AP operation with themultiple APs. For example, the STA may receive, from AP1, a firstmultiple AP association response frame that includes an indicatorindicating acceptance or rejection of the multiple AP operation withAP1. The STA may then receive, from AP2, a second multiple APassociation response frame that includes an indicator indicatingacceptance or rejection of the multiple AP operation with AP2. Themultiple AP association response frames may be received at the STA in apredetermined order or a random order until all the multiple APassociation response frames are received correctly. For example, themultiple AP association response frames may be received in the order ofAPs listed in the multiple AP service set. The multiple AP associationresponse frames received at the STA may not overlap each other so thatthe STA has time to decode the multiple AP association response framefrom AP1 before the STA receives the next multiple AP associationresponse frame from AP2.

At step 885, the STA may transmit multiple AP association acknowledge(ACK) frames to the multiple APs that transmitted the multiple APassociation response frames if the multiple AP association responseframes are correctly received (regardless of whether the multiple APassociation response frames include acceptance or rejection for themultiple AP operation). The STA may also transmit multiple APassociation negative acknowledge (NACK) frames to the multiple APs thattransmitted the multiple AP association response frames if the multipleAP association frames are not correctly received (regardless of whetherthe multiple AP association response frames include acceptance orrejection for the multiple AP operation). For example, if a firstmultiple AP association response frame from AP1 is correctly decoded atthe STA, the STA may transmit, to AP1, a first multiple AP associationACK frame. If the first multiple AP association response frame from AP1is not correctly decoded at the STA, the STA may transmit, to AP1, afirst multiple AP association NACK frame. Similarly, if a secondmultiple AP association response frame from AP2 is correctly decoded atthe STA, the STA may transmit, to AP2, a second multiple AP associationACK frame. If the second multiple AP association response frame from AP2is not correctly decoded at the STA, the STA may transmit, to AP2, asecond multiple AP association NACK frame.

At step 890, once the STA received the multiple AP association responseframes from the APs in the multiple AP service set and the multiple APassociation response frames indicate acceptance of the multiple APoperation with the APs, the STA may initiate the multiple AP operationwith the APs by transmitting and/or receiving data to and/or from theAPs. Specifically, if the first multiple AP association response framereceived from AP1 indicate acceptance of the multiple AP operation withAP1 and the second multiple AP association response frame received fromAP2 indicate acceptance of the multiple AP operation with AP2, the STAmay transmit and/or receive data with the AP1 and AP2, for example,using coordinated orthogonal frequency-division multiple access (OFDMA)or coordinated nulling. The STA may also perform, with the multiple APs(e.g., AP1 and AP2), joint transmission/reception, HARQ feedback, MIMO,dynamic AP selection, and multiple AP roaming.

FIG. 9 illustrates an example multiple AP association 900 initiated by aSTA, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 9 , a STA 902 may identifycandidate APs (e.g., AP1 914 a and AP2 914 b) using the existing IEEE802.11 probe request/probe response mechanism and associate with asingle AP (e.g., AP1 914 a). For example, the STA 902 may identify thecandidate APs (e.g., AP1 914 a, AP2 914 b) in its proximity based onactive scanning as described above. The candidate APs (e.g., AP1 914 aand AP2 914 b) may be included in a multiple AP service set or multipleAP service set that provide the support for the multiple AP association,transmission, and/or reception between the STA and the candidate APs. Inan example, AP1 914 a may be identified as a primary AP and AP2 914 bmay be identified as a secondary AP in the same multiple AP service set.Once the candidate APs 914 a, 914 b are identified, the STA 902 maytransmit probe request frames 905 a, 905 b to the APs 914 a, 914 b andreceive probe response frames 910 a, 910 b from the APs 914 a, 914 b.The STA 902 may then perform authentication and association procedureswith an AP (e.g., AP1 914 a). For example, the STA may transmit anauthentication request frame 915 to AP1 914 a and receive anauthentication response frame 920 from AP1 914 a. Once the STA 902 isauthenticated by AP1 914 a, the STA 902 may send an association requestframe 925 to AP1 914 a and receive an authentication response frame 930from AP1 914 a. The STA 902 may then initiate a multiple AP associationwith information on one or more suitable candidate APs, f or example, inthe multiple AP service set. The candidate APs (e.g., AP1 914 a and AP2914 b) may be identified from probe response frames 910 a, 910 b fromother APs during the probe request/probe response phase.

In case that the STA 902 is first associated with the primary AP (e.g.,AP1 914 a) as illustrated in FIG. 9 , the STA 902 may send a multiple APassociation request frame 935 a (or announcement frame) to its primaryAP (e.g., AP1 914 a) with information on the candidate APs (e.g., AP1914 a and AP2 914 b) or multiple APs in the multiple AP service set.Alternatively or additionally, the STA 902 may send a multiple APassociation request frame 935 b (or announcement frame) to the candidateAP (e.g., AP2 914 b) with information on the other AP (e.g., AP1 914 a)or other multiple APs in the multiple AP service set. The STA 902 maysequentially add one new AP to its own multiple AP service set. The APs914 a, 914 b may track one or more STAs (e.g., STA 902) connected to orassociated with each of the multiple AP service sets and may use thisinformation to schedule the multiple AP schemes or multiple AP operationwith the STAs.

In an embodiment, the STA 902 may send an indication of a priority inwhich the multiple APs (e.g., AP1 914 a and AP2 914 b) are to beassociated in the multiple AP service set, including the capability ofchanging the primary AP (e.g., AP1 914 a) to secondary AP (e.g., AP2 914b), tertiary AP, or so forth, as well as indicating the new primary AP.The priority order may be explicitly signaled in the multiple APassociation request frames 935 a, 935 b, or the AP priority may beimplicitly signaled by the order in which the AP identifiers appear inthe multiple AP association request frames 935 a, 935 b. On receipt ofthe multiple AP association request frames 935 a, 935 b, the APs 914 a,914 b may perform some AP coordination procedures 940, such astransferring security information from the primary AP (e.g., AP1 914 a)to the secondary AP (e.g., AP2 914 b) and/or ensuring that the AP (e.g.,AP1 914 a) can only connect to the secondary AP (e.g., AP2 914 b) toensure that they are able to coordinate in the manner requested. Thismay involve higher layer signaling through a backhaul or an APcoordinator. Alternatively or additionally, the primary AP (e.g., AP1914 a) may send an OTA signal to the secondary AP (e.g., AP2 914 b) withdetails of the coordination request and type of data needed.

The APs 914 a, 914 b may then send multiple AP association responseframes 945 a, 945 b to the STA 902 as illustrated in FIG. 9 . In oneembodiment, each AP 914 a, 914 b may send an independent multiple APassociation response frame 945 a, 945 b to the STA 902. The multiple APassociation response frames 945 a, 945 b may be sent in a manner thatensures separability in code, time, frequency and/or space.Alternatively or additionally, the multiple AP association responseframes 945 a, 945 b may be sent using the downlink multiple AP scheme asrequested (e.g., joint transmission or as a test of the system). Themultiple AP association response frames 945 a, 945 b may accept themultiple AP scheme requested by the STA 902 in the multiple APassociation request frames 935 a, 935 b, or reject the multiple APscheme requested by the STA 902 in the multiple AP association requestframes 935 a, 935 b. Alternatively or additionally, the multiple APassociation response frames 945 a, 945 b may suggest an alternativescheme to the scheme requested by the STA 902.

The STA 902 may then reply with a multiple AP association ACK frame 950a, 950 b to both APs 914 a, 914 b to ensure that both APs 914 a, 914 bknow that the STA 902 is now ready for the multiple APtransmission/reception setup. Although it is not illustrated in FIG. 9 ,on a condition that one of the APs 914 a, 914 b is unable to accept themultiple AP association request (e.g., 935 a or 935 b) and does not senda multiple AP association response (e.g., 945 a or 945 b), the multipleAP association ACK frame (e.g., 950 a or 950 b) may ensure that theother AP (e.g., 914 a or 914 b) is aware that it is the primary AP andshould not set up a multiple AP transmission/reception procedure 955.For example, assuming that AP2 914 b is unable to accept the multiple APassociation request 935 b and does not send the multiple AP associationresponse 945 b (not illustrated in FIG. 9 ), the multiple AP associationACK frame 950 a may ensure that AP2 914 b is aware that AP1 914 a is theprimary AP and AP2 914 b should not set up a multiple APtransmission/reception procedure 955. This may enable a fall back tosingle AP association if the multiple AP association procedure isunsuccessful.

In an embodiment, an AP may transmit a multiple AP service set elementto indicate that the AP is part of a multiple AP service set (SS). Beingpart of a multiple AP SS may imply that the AP is capable of conductingmultiple AP transmissions/receptions. Such capabilities may also beexplicitly indicated.

FIG. 10 illustrates an example multiple AP service set (SS) element1000, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 10 , the multiple AP SS element1000 may comprise element ID 1005 and element ID extension fields 1015,a length field 1010, a multiple AP SS AP count field 1020, and multipleAP SS AP 1-N fields 1025, 1030. A combination of the element ID 1005 andelement ID extension fields 1015 may indicate that the current elementis a multiple AP SS element 1000. The length field 1010 may be used toindicate the length of the multiple AP SS element 1000. The multiple APSS AP count field 1020 may indicate how many information fields areincluded in the multiple AP SS element 1000. In an embodiment, if onlyone field is contained, such as the information field regarding thetransmitting STA, then the multiple AP SS AP count field 1020 may beomitted. In other embodiments, this multiple AP SS AP count field 120may be used to indicate the size of the multiple AP service set, such asby indicating how many APs are contained in the multi-STA service set.

The N multiple AP SS AP fields 1020, 1030 may comprise informationregarding each of the APs that are a part of the multiple AP serviceset. In an embodiment, the number of fields may be indicated in themultiple AP SS AP count field 1020. In other embodiments, only one APmay be contained in the information. The information included in the oneor more subfields of the N multiple AP SS AP fields 1020, 1030 mayinclude, for each of the APs, the AP ID 1050 (such as MAC address of theAP or other identifier or identifiers), the master AP indicator 1055(e.g., an indication of whether the AP included in this field is themaster or primary AP or a slave AP, various multiple AP capabilityindications. Examples of the various multiple AP capabilities mayinclude, but are not limited to, capability to support multiple AP jointtransmission 1060, multiple AP HARQ 1065, multiple AP MIMO 1070,multiple AP MU-MIMO 1075, dynamic AP selection 1080, multiple AP roaming1085 and multiple AP coordinated beamforming 1090, and order (e.g., asubfield that may indicate the order of the each member AP beingidentified in the multiple AP service set). In embodiments, the ordersubfield associated with a member AP may indicate the order of the APwithin the multiple AP service set.

The designs, fields and subfields just described are examples and may beimplemented using existing or new fields, subfields, elements, MAC/PLOPheaders, or any part of a transmitted frame.

An AP may include a multiple AP SS element, for example, in its beacon,short beacon, probe response, association response, or fast initial linksetup (FILS) discovery frame, to indicate that the AP is a part of amultiple AP service set. The AP may also indicate its own multiple APcapabilities, including, for example, support for multiple AP jointtransmission, multiple AP HARQ, multiple AP MIMO, multiple AP MU-MIMO,dynamic AP selection, multiple AP roaming and multiple AP coordinatedbeamforming. The AP may also indicate whether it is a master(coordinator) or slave AP within the multiple AP service set. The AP mayalso indicate whether the field is related to the transmitting AP orreceiving AP. In addition, the multiple AP SS element may includeinformation of one or more member APs in the same multiple AP serviceset. The multiple AP SS element may provide information regarding othermember APs' multiple AP capabilities, such as whether they supportmultiple AP joint transmission, multiple AP HARQ, multiple AP MIMO,multiple AP MU-MIMO, dynamic AP selection, multiple AP roaming andmultiple AP coordinated beamforming. The multiple AP SS element may alsoindicate whether other member APs are master or slave APs. In someembodiments, the AP may also provide information regarding one or moreor all other member APs in the same multiple AP SS in another element,such as an indication using one of the reserved bits in the reducedneighbor report element or neighbor report elements, includingindication of the IDs (BSSIDs, SSIDs), capabilities or their beingmaster or slave APs. In addition, the member APs in the multiple APservice set may be ordered in such a way that the order of the memberAPs included in the multiple AP SS element is the multiple AP SS (MASS),which may be identified by an SSID or a MASSID and/or provided in themultiple AP SS element.

A non-AP STA may monitor the medium for, for example, beacons, shortbeacon, or FILS discovery frames, to discover the appropriate AP orMASS. The non-AP STA may send a probe request targeting an AP and/orMASS in order to discover one or more APs within its range that aremembers of a particular MASS. A non-AP STA may include a multiple APcapabilities element in the probe request frames, which may imply thatit can support multiple AP transmission and/or reception. It may includethe STA's capabilities for supporting multiple AP transmissions, such assupporting multiple AP joint transmission, multiple AP HARQ, multiple APMIMO, multiple AP MU-MIMO, dynamic AP selection, multiple AP roaming andmultiple AP coordinated beamforming. Such capabilities may also beincluded in a capabilities element, such as an extremely high throughput(EHT) capabilities element.

A non-AP STA that receives a multiple AP SS element from an AP, whichmay be included in a beacon, short beacon, probe response, associationresponse frame, FILS discovery frame, or any other kind of frame, mayunderstand that the AP is part of a multiple AP service set and thatcertain multiple AP transmission capabilities may be supported by theAPs in the multiple AP service set. In addition, it may discover theidentities and/or the capabilities of one or more member APs in the samemultiple AP SS (MASS).

After discovering the information for one or more member APs of the sameMASS, the STA may send another frame, such as a probe request frame,multiple AP probe request or MASS probe request, that may include theSSID, the MASS ID and/or one or more IDs, such as MAC address, of themember APs that the STA is targeting. In other embodiments, the STA maysend a probe request frame targeting the MASS ID, and the probe requestframe may include a bit map with one or more bits set to 1, which mayindicate a member AP that may be associated with the order of the memberAP in the MASS, for which a probe response is being requested. The proberequest frame may also include an indication that it is a probe requestfor a MASS. A member AP of the MASS, after receiving the probe requesttargeted at the MASS ID, including its MAC address, or identified by abit 1 in the bitmap, may respond with a probe response. In otherembodiments, a member AP of the MASS, after receiving the probe requesttargeted at the MASS ID, may respond with a probe response.

Alternatively or additionally, the probe request sent by the non-AP STAmay also include the transmit power used to transmit the probe requestand a received power threshold. Any targeted member AP, such as from atargeted MASS, that received the probe request frame below the receivedpower threshold may ignore the probe request frame. Otherwise, the APmay respond with a probe response.

The non-AP STA may have a list of parameters, such as MCS, RSSI or otherchannel quality parameters, of member APs of a MASS that it discoveredafter monitoring the medium and receiving targeted probe responses,beacons, short beacons, FILS Discovery frames, or other type of framesfrom the member APs. It may select one or more member APs in the MASS tobe its designated APs. One of the designated APs may serve as theprimary AP while one or more APs may serve as one or more secondary APsfor the STA.

If the AP and/or the MASS satisfies requirements of the non-AP STA, itmay send an association request or a multiple AP association request tothe selected AP, including a multiple AP selection element. FIG. 11illustrates an example multiple AP selection element 1100, which may beused in combination of any of other embodiments described herein.

The multiple AP selection element 1100 may include element ID 1105 andelement ID extension fields 1115, a length field 1110, a multiple APcapabilities field 1120, a multiple AP service requested field 1125, anAP information count field 1130, and N AP information fields 1135, 1140.A combination of the element ID 1105 and element ID extension fields1115 may indicate that the current element is a multiple AP selectionelement 1100. The length field 1110 may be used to indicate the lengthof the multiple AP selection element 1100. The multiple AP capabilitiesfield 1120 may be used to indicate the capabilities of the STA formultiple AP transmissions/reception, including, for example, multiple APjoint transmission, multiple AP HARQ, multiple AP MIMO, multiple APMU-MIMO, dynamic AP selection, multiple AP roaming and multiple APcoordinated beamforming. The multiple AP service requested field 1125may indicate the multiple AP services that are being requested by thetransmitting AP, including multiple AP joint transmission, multiple APHARQ, multiple AP MIMO, multiple AP MU-MIMO, dynamic AP selection,multiple AP roaming and multiple AP coordinated beamforming. The APinformation count field 1130 may indicate the number of AP informationfields that are included. The N AP information fields 1135, 1140 mayinclude information on member APs for which multiple AP service is beingrequested. Examples of the N AP information fields 1135, 1140 mayinclude, but are not limited to, an AP ID 1150, a primary/secondaryindicator 1155, a received power/channel quality indication 1160 and amandatory indicator 1165. The AP ID 1150 may be a MAC address or orderof the member AP in the MASS. The primary/secondary indicator 1155 mayindicate a request for the AP to be accepted as a primary or secondaryAP, if applicable. The received power/channel quality indication field1160 may indicate the channel quality between the AP and thetransmitting STA, such as RSSI, RSRP or RCPI. The mandatory indicator1165 may indicate whether the transmitting STA is requesting that thetarget AP be mandatory or optionally accepted. Alternatively oradditionally, if a STA does not have sufficient information regardingthe member APs of the targeted MASS, it may indicate, in the multiple APselection element 1100, that it is requesting information on othermember APs that support multiple AP services. The AP may respond with aframe, such as a probe response or beacon, short beacon, or FILSdiscovery frame, which may include a multiple AP element to provide therequested information.

In embodiments, the non-AP STA may send one or more association requestframes or multiple AP association request frames to all desired memberAPs that include the multiple AP selection element. After receiving theassociation request frame or the multiple AP association request frame,the AP may decide whether it will accept the association as aprimary/secondary AP as requested. Alternatively or additionally, theprimary AP identified in the probe request frame may forward theassociation request to any secondary APs that are identified in theassociation/authentication request or multiple APassociation/authentication request. If the primary AP is a slave AP, theprimary AP may forward the association/authentication request for one ormore secondary APs to the master AP, which may conduct association withthe secondary APs on the STA's behalf. Such forwarding and respondingmay take place on the wireless medium, use wired backbones, use adifferent band, or use frequency channels. Once the secondary APsrespond, the primary AP may send a multiple APassociation/authentication response frame to the requesting STA. Themultiple AP association/authentication response frame may include thestatus as to whether the association/authentication with the primary APand the secondary APs is successful.

In one embodiment, a non-AP STA may request association with a first AP,such as a selected primary AP. Once the STA is associated with theprimary AP, the STA may receive a list of other member APs of the sameMASS in the AP's beacon, short beacon, probe response, associationresponse, or other type of frame. The STA may send one or more proberequest frames targeting the SSID of the MASS and/or one or more IDs,such as MAC addresses, of the member APs that the STA is targeting. Inanother embodiment, the STA may send a probe request frame targeted atthe MASS ID, and the probe request frame may include a bit map with eachbit set to 1, which may indicate a member AP that may be associated withthe order of the member AP in the MASS for which a probe response isbeing requested. The probe request frame may also include an indicationthat it is a probe request for a MASS. A member AP of the MASS, afterreceiving the probe request frame that is at least one of targeted atthe MASS ID and/or its MAC address or identified by a bit 1 in thebitmap, may respond with a probe response frame.

Alternatively or additionally, the probe request frame sent by thenon-AP STA may also include the transmit power used to transmit theprobe request and a received power threshold. Any targeted member APthat received the probe request frame below the received power thresholdmay ignore the probe request frame.

The non-AP STA may have a list of parameters, such as MCS, RSSI or otherchannel quality parameters of member APs of a MASS that it discoveredafter monitoring the medium and receiving targeted probe response frame.The STA may select one or more member APs in the MASS to be itssecondary APs.

The non-AP STA may subsequently send a frame, such as a multiple APassociation request frame or a multiple AP service negotiation frame, toits primary AP. The multiple AP association request frame or multiple APservice negotiation frame may contain the multiple AP selection element,which may indicate a request for certain multiple AP service and/or anumber of secondary APs. The primary AP may then decide whether toprovide the multiple AP service to the STA. Alternatively oradditionally, such decision may be made at the master AP of the MASS.The primary AP may forward the multiple AP request to any secondary APsthat are identified in the multiple AP association request frame ormultiple AP negotiation frame. If the primary AP is a slave AP, it mayforward the multiple AP association request frame or multiple AP servicenegotiation request for one or more secondary APs to the master AP,which may then conduct the multiple AP service negotiation with thesecondary APs on the STA's behalf. Such forwarding and responding maytake place on the wireless medium (e.g., OTA), use wired backbones, usea different band, or use different frequency channels. Once thesecondary APs respond, the primary AP may send the multiple APassociation response frame or multiple AP service negotiation responseframe to the requesting STA including the status that indicates: (1)whether the multiple AP service will be provided; (2) which multiple APservice will be provided; (3) which member APs are successfully added asthe STA's secondary APs; and (4) which multiple AP service will beprovided.

For coordinated OFDMA, in embodiments, a STA may autonomously estimateif the STA is located in a BSS edge (i.e. BSS edge STA) or a BSS center(i.e. BSS center STA) relative to its primary or serving BSS. Forexample, path loss, geography or BSS position may be used for theestimation. However, in a dense network, such as an apartment buildingwith many overlapping basic service sets (OBSSs), the interactionbetween the BSSs may determine if a STA needs to be placed in theBSS-edge group. This may require a procedure that involves the BSSs andthe STA. The terms BSS center STA and cell center STA may beinterchangeably used throughout this disclosure. The terms BSS edge STAand cell edge STA may be interchangeably used throughout thisdisclosure.

In an embodiment, multiple APs such as AP1 and AP2 may need tocoordinate to decide to implement the coordinated OFDMA. In one example,AP1 may review the multiple AP associated STAs (i.e. STAs associatedwith multiple APs) and identify AP2 as an AP to coordinate with. The APsmay automatically assign any STAs that are identified as multiple APassociated STAs as the BSS edge STAs. Alternatively or additionally, theAPs may coordinate to send information to assist the STAs in estimatingwhether they are BSS edge or BSS center STAs.

In one embodiment, following steps may be performed for the coordinatededge/center discovery. At step 1, AP1 may send AP2 a coordinationrequest frame (e.g., over the air or through a backhaul link). At step2, AP1 may receive a coordination acknowledgement frame from AP2 if itis willing and able to coordinate with AP1. At step 3, AP1 may send anull data packet announcement (NDPA) frame to the AP2 and STAs in itsBSS (i.e. both non-multiple AP associated STAs and multiple APassociated STAs). In one example, the AP2 may send an NDPA frame as anACK to AP1 and to announce the upcoming NDP to STAs in its BSS (i.e.both non-multiple AP associated STAs and multiple AP associated STAs).This procedure may be used for general coordination or jointtransmission. Alternatively or additionally, the steps described in thisembodiment may be replaced by the multiple AP association proceduresdescribed above.

At step 4, AP1 and AP2 may send NDPs to the STAs in their BSSs. In oneembodiment, AP1 and AP2 may send the NDPs at the same time. In such anembodiment, the difference in received RSSI between the NDPA and NDP mayindicate if a STA is a BSS edge STA or a BSS center STA. If thedifference in RSSI between the NDPA and NDP is less than a threshold,then the STA may be considered to be a BSS center STA because it mayindicate that the signal from AP2 is not received. If the difference inRSSI between the NDPA and NDP is greater than a threshold, then the STAmay be considered to be a BSS edge STA.

In another embodiment, the NDP frames from the APs may be orthogonal. Inone example, the NDP frames may be orthogonal in time with the NDP fromthe AP2 sent a SIFS after the NDP from AP1. In another example, the NDPframes may be orthogonal in frequency (e.g., interlaced in frequency).The positions of the NDP frames may depend on NDP subcarrier spacing(e.g., Ng). As an example, if Ng equals four (NG=4) with interlace valuewhich equals two (interlace value=2), then AP1 may send its NDP onsubcarriers 0, 4, 8, . . . while AP2 may send its NDP on subcarriers 2,6, 10, . . . . In another example, the NDP frames may be sent asorthogonal or semi-orthogonal sequences.

Each STA may measure the RSSI of the NDP signal from each AP and thenestimate the RSSI difference/ratio between the signal from its primaryAP (e.g., AP1) and its secondary AP (e.g., AP2). If the RSSIdifference/ratio is less than a threshold, then the STA may beconsidered to be a BSS edge STA. If the RSSI difference/ratio is greaterthan a threshold, then the STA may be considered to be a BSS center STA.

At step 5, the STAs, upon identifying whether they are BSS edge or BSScenter STAs, may feedback this information to the APs. In one example,the AP may poll each STA for the feedback information. In anotherexample, the STAs may use the NDP feedback report to provide thefeedback information. In this example, the AP may send an NDP feedbackreport poll (NFRP) trigger frame with parameters that indicate a requestfor the information whether the STA is a BSS center or edge STA. Inanother example, the NFRP trigger frame may transmit one or moreadditional parameters indicating the cut-off values for cell center/celledge classification (e.g., edge Tx power, signal-to-interference ration(SIR) cut-off value or RSSI difference). At SIFs duration after thereceipt of the NFRP trigger frame, the STAs may transmit the requiredinformation in an NDP feedback report. In an example, only STAs of acertain type may transmit the information, implying that any STA thatdoes not transmit the NDP feedback report is of the other type. The APsmay recognize the STAs that transmitted the NDP feedback reports as theBSS center STA/BSS edge STAs and the STAs that did not transmit the NDPfeedback reports as the BSS edge STAs/BSS center STAs. In anotherexample, all STAs may send feedback with information specifying the typeof STA (e.g., BSS edge or center STA). In another example, the STAs mayuse an HE-CQI report to feedback the RSSI or RSSI difference. This maybe for a single spatial-temporal subband (STS) and averaged over theentire bandwidth.

From the STA point of view, the STA that is associated with multiple APsand identifies primary and secondary APs, may first identify a multipleAP discovery NDPA from AP1. The STA may identify the multiple APdiscovery NDPA from AP2. The STA may then estimate the requiredmeasurement from the NDP. For example, the STA may identify SIR NDP andestimating SIR (RSSI1-RSSI2; per tone or averaged). The STA may identifySIR cut-off for center/edge determination from NFRP. The STA may sendsignals to the APs that includes center/edge indicators. Alternativelyor additionally, the STA may send SIR in an HE-CQI frame and allow theAPs to decide whether the STA is the BSS center or edge STA

FIG. 12 illustrates an example of scheduled/random access coordinatedOFDMA 1200, which may be used in combination of any of other embodimentsdescribed herein. The data transmission may be scheduled or randomaccess coordinated OFDMA. For the scheduled data transmission in thedownlink and uplink, APs 1214 a, 1214 b may schedule the appropriateSTAs in the corresponding resources with transmit power control orcoordinated beamforming/nulling (CB/N). Assuming that AP1 1214 a isassigned RU1 1205 and AP2 1214 b is assigned RU2 1220, cell edge STAsmay be assigned by AP1 1214 a in RU1 1205, cell edge STAs may beassigned by AP2 1214 b in RU2 1220 and cell center STAs may be assignedby AP1 1214 a in both RU1 1205 and RU2 1210 and by AP2 1214 b in bothRU1 1215 and RU2 1220. The cell center STAs may transmit as is withpower control to limit the amount of interference with the cellcenter/edge STAs of the other BSS. The cell center STAs may transmitusing a CB/N scheme, as described in more detail below, to limit theamount of interference with the cell center/edge STAs of the other BSS.

For random access (RA) data transmission in the uplink, the APs 1214 a,1214 b may use coordinated uplink OFDM random access. As illustrated inFIG. 12 , AP1 1214 a may allow both edge and center STAs to set RU1 1205as an eligible RA-RU (e.g., an RA-RU for which the HE STA is capable ofgenerating an HE TB PPDU). AP1 1214 a may set RU2 1210 as an eligibleRA-RU for center STAs only. Similarly, AP2 1214 b may allow both edgeand center STAs to set RU2 1220 as an eligible RA-RU (e.g., an RA-RU forwhich the HE STA is capable of generating an HE TB PPDU). AP2 1214 b mayset RU1 1215 as an eligible RA-RU for center STAs only.

For simplified signaling, in some embodiments, center and edge STAs maybe manually assigned to a group ID. The group ID may be assigned tospecific RA-RUs. Alternatively or additionally, cell edge and centerSTAs may be assigned to specific AIDs/AID groups, and RA-RUs may beassigned to those specific AIDs/AID groups.

FIG. 13 is a system diagram of an example 1300 of multiple APassociation, cell center/cell edge discovery and data transmission,which may be used in combination of any of other embodiments describedherein. In this example, it is assumed that STA1 1302 a is a BSS centerSTA relative to AP1 1314 a, STA2 1302 b is a BSS edge STA relative toAP1 1314 a, STA3 1302 c is a BSS center STA relative to AP2 1314 b, andSTA4 1302 d is a BSS edge STA relative to AP2 1314 b. It is also assumedthat STA2 1302 b and STA4 1302 d are located in cell edges from AP1 1314a and AP2 1314 b. As illustrated in FIG. 13 , during the multiple APassociation phase 1301, STA1 1302 a may receive a beacon frame 1305 afrom AP1 1314 a and perform the association procedure with AP1 1314 a.STA2 1302 b located in the cell edges from AP1 1314 a and AP2 1314 b mayreceive both the beacon frames 1305 a, 1305 b from AP1 1314 a and AP21314 b and perform multiple AP association procedure with AP1 1314 a andAP2 1314 b as described above. Similarly, STA3 1302 c may receive abeacon frame 1305 b from AP2 1314 b and perform the associationprocedure with AP2 1314 b. STA4 1302 d located in the cell edges fromAP1 1314 a and AP2 1314 b may receive both the beacon frames 1305 a,1305 b from AP1 1314 a and AP2 1314 b and perform multiple APassociation procedure with AP1 1314 a and AP2 1314 b as described above.

During or after the multiple AP association phase 1301, AP1 1314 a andAP2 1314 b may perform AP coordination procedures 1302 to ensure thatthe APs 1314 a, 1314 b are able to provide multiple AP operation to STA21302 b and STA 41302 d. The AP coordination procedures 1302 may beperformed in a centralized manner or a distributed matter. In oneexample, AP1 1314 a and AP2 1314 b may negotiate fractional frequencyreuse (FFR) through a centralized controller that communicates with AP11314 a and AP2 1314 b via backhaul links or OTA signals as illustratedin step 1320. In another example, AP1 1314 a and AP2 1314 b may directlynegotiate fractional frequency reuse (FFR) via the backhaul link or OTAsignals as illustrated in step 1325. Specifically, AP1 1314 a may send acontrol message to AP2 1314 b and receive an ACK from AP2 1314 b for theFFR negotiation.

During the center/edge discovery phase 1303, AP1 1314 a may send an NDPAframe 1330 a to AP2 1314 b and STAs 1302 a, 1302 b in its BSS.Similarly, AP2 1314 b may send an NDPA frame 1330 b to AP1 1314 a andSTAs 1302 c, 1302 d in its BSS. AP1 1314 a may then send ansignal-to-noise interference ration (SIR) NDP frame 1335 a to STAs 1302a, 1302 b in its BSS so that STAs 1302 a, 1302 b may estimate the SIR,for example, the RSSI difference between the received NDPA frame 1330 aand the received SIR NDP frame 1335 a. Similarly, AP2 1314 b may thensend an SIR NDP frame 1335 b to STAs 1302 c, 1302 d in its BSS so thatSTAs 1302 c, 1302 d may estimate the SIR, for example, the RSSIdifference between the received NDPA frame 1330 b and the received SIRNDP frame 1335 b. At this point, STAs 1302 a, 1302 b, 1302 c, 1302 d mayidentify whether they are cell edge or center STAs, for example, basedon the estimated SIR. AP1 1314 a may send an NDP feedback report poll(NFRP) frame 1340 a to STA1 1302 a and STA2 1302 b to request theinformation whether the STAs 1302 a, 1302 b are cell center or edgeSTAs. Upon receiving the NFRP frame 1340 a, STA1 1302 a may respond anNDP feedback frame 1345 a indicating that STA1 1302 a is the cell centerSTA and STA2 1302 b may respond an NDP feedback frame 1345 b indicatingthat STA2 1302 b is the cell edge STA. Similarly, AP2 1314 b may alsosend an NFRP frame 1340 b to STA3 1302 c and STA4 1302 d to request theinformation whether the STAs 1302 c, 1302 d are cell center or edgeSTAs. Upon receiving the NFRP frame 1340 b, STA3 1302 c may respond anNDP feedback frame 1350 a indicating that STA3 1302 c is the cell centerSTA and STA4 1302 d may respond an NDP feedback frame 1350 b indicatingthat STA4 1302 d is the cell edge STA.

During the data transmission phase 1304, AP1 1314 a and AP2 1314 b maytransmit random access trigger frames to the STAs 1302 a, 1302 b, 1302c, 1302 d to allocate resource units (RUs) for random access. Forexample, AP1 1314 a may send a UL-OFDMA random access (UORA) triggerframe 1355 a to STA1 1302 a and STA2 1302 b to indicate that STA1 1302 a(i.e. cell center STA) is allocated to use RU1 and RU2 and STA2 1302 b(i.e. cell edge STA) is allocated to use RU1. Upon receiving the UORAtrigger frame 1355 a, STA1 1302 a may transmit data using RU1 and RU21360 a, and STA2 1302 b may transmit data to one or more APs 1314 a,1314 b using RU1 1365. Similarly, AP2 1314 b may send a UORA triggerframe 1355 b to STA3 1302 c and STA4 1302 d to indicate that STA3 1302 c(i.e. cell center STA) is allocated to use RU1 and RU2 and STA4 1302 d(i.e. cell edge STA) is allocated to use RU1. Upon receiving the UORAtrigger frame 1355 b, STA3 1302 c may transmit data using RU1 and RU21370, and STA4 1302 d may transmit data to one or more APs 1314 a, 1314b using RU1 1375.

In one embodiment, for coordinated OFDMA, a set of guard resources orguard RUs may be negotiated between resources allocated for coordinatedOFDMA. This may allow for some inter-carrier interference without theneed for tight synchronization.

FIG. 14 illustrates an example guard band 1400 for fractionalcoordinated OFDMA, which may be used in combination of any of otherembodiments described herein. As illustrated in FIG. 14 , for AP1, RU11405 is allocated to the cell edge and center STAs and RU2 1415 isallocated to the cell center STAs. In this example, the resourcesallocated to the cell edge STAs (i.e. RU1 1405) may have a set of guardresources or guard RUs 1410. Similarly, for AP2, RU2 1430 is allocatedto the cell edge and center STAs and RU1 1415 is allocated to the cellcenter STAs. The resources allocated to the cell edge STAs (i.e. RU21430) may have a set of guard resources or guard RUs 1430.

In one embodiment, cyclic prefix (CP) length modification may be used toensure that CP length is larger than the sum of: (1) maximum timingoffset of the STAs associated with BSS1; (2) the maximum timing offsetof the STAs associated with BSS2; and (3) the maximum channel impulseresponse (CIR) length of BSS1 and BSS2. Although it is not described inthe above example, this scheme is applicable to more than two BSSs bysumming up the parameters for all BSSs in the coordinated BSS set.

In IEEE 802.11ax, a STA that transmits an HE TB PPDU in response to atriggering PPDU, such as a PPDU that includes a trigger frame or a framehaving a triggered response scheduling (TRS) control subfield, from anAP, may ensure that the arrival time of the HE TB PPDU at the AP iswithin ±0.4 μs of TXTIME+aSIFSTime+RTD from the transmission start timeof the triggering PPDU. Here, TXTIME may be that of the triggering PPDUand RTD may be the round-trip delay between the AP and the STA. In oneembodiment, this may be modified in coordinated OFDMA to ensure that theexisting CP length is adequate (e.g., the tolerance time may be halvedfor a 2 BSS coordination set). Additionally or alternatively, thetolerance time may be kept constant but the maximum CP length may bedoubled for a 2 BSS coordination set. In a simple example, rather than 3possible CP lengths in IEEE 802.11ax, six possible CP lengths may beused.

In another embodiment, each AP may calibrate the response timing of theSTAs in its BSS and send timing advance/timing retardation requests toeach STA in order to reduce the timing difference between the STAs. Themaximum timing differences may then be sent to each AP to enable each APto estimate the CP to be used. The information may be sent via abackhaul link to a centralized AP, which may estimate a common CP andsend this information to each AP. Alternatively or additionally, theinformation may be sent via a backhaul link to a centralized AP, whichmay estimate BSS and/or STA specific CPs that may be sent to each AP.Alternatively or additionally, the information may be sent to each AP inthe coordination set and the AP may then independently set its CPs. Theinformation may be sent via a backhaul link or over the air (OTA)signals. For the OTA, in one example, the information may be transmittedin a special frame or in the extremely high throughput (EHT) preamble byedge STAs to allow neighboring APs in the set to overhear theinformation.

In one embodiment, a coordinated OFDMA synchronization trigger frame maybe sent from a master AP. The master AP may be a separate AP thatcoordinates all the APs in the coordination set, such as the set of BSSsinvolved in the coordinated OFDMA transmission. Alternatively oradditionally, the master AP may be one of the APs in the coordinationset. This AP may be pre-determined, selected randomly or elected by theAPs in the coordination set.

In another embodiment, a coordinated OFDMA synchronization triggerand/or sequence may be used. On receipt of a master trigger frame, allthe APs in the group may send triggers to their respective STAs with apredetermined timing tolerance to ensure orthogonality. In someembodiments, the master trigger frame may be sent before any individualAP sends an individual trigger frame. Additionally or alternatively, themaster trigger frame may be sent at configurable intervals. Theindividual trigger frames may be sent at specific times after the mastertrigger frame is received. The intervals may be configured statically ordynamically. If they are configured dynamically, an individual AP mayrequest a master trigger transmission on a condition that itsinter-carrier interference (ICI) exceeds a pre-determined threshold.

In another embodiment, the master AP may send a specific synchronizationsignal or sequence to initiate the start of the individual AP triggers,rather than a separate master trigger frame. In some embodiments, themaster AP may send a trigger frame to all the edge STAs and request acalibration transmission. The other coordinating AP may then calibratethe start of its trigger frame based on the timing difference betweenthe receipt of the end of the master trigger frame and the receipt ofthe start of the response of its edge STA. As such, on receipt of themaster trigger frame from the master AP, it may be able to transmit itstrigger frame to ensure that the transmitted frames within its BSS aresynchronized with the master AP trigger.

In another embodiment, the master trigger frame may comprise informationregarding the maximum length of the expected trigger frame expected. Ifthe trigger frame for each AP is less than a required length, the AP mayadd padding to the trigger frame to ensure that the transmissions beginin such a manner as to ensure orthogonality. In some embodiments, thepadding may be AP specific to provide a timing advance/timingretardation and allow for synchronization of the transmissions in themultiple BSSs.

Embodiments for coordinated beamforming/coordinated nulling (CB/CN) aredescribed herein. In coordinated beamforming, the transmitting device(or STA), desired device (or STA) and non-desired device (or STA) maydetermine the procedure used and the type of feedback requested. Variousarchitectures and embodiments are described herein that may be used.

FIG. 15 illustrates an example architecture 1500 for downlink-downlinkCB/CN, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 15 , the transmitting devicesmay be both AP1 1514 and AP2 1514 b, and the desired and non-desireddevices may be both STA1 1502 a and STA2 1502 b for thedownlink-downlink CB/CN.

FIG. 16 illustrates an example architecture 1600 for uplink-uplinkCB/CN, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 16 , the transmitting devicesmay be both STA1 1602 a and STA2 1602 b, and the desired and non-desireddevices may be both AP1 1614 a and AP2 1614 b.

FIG. 17 illustrates an example architecture 1700 for uplink-downlinkCB/CN, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 17 , for the uplink-downlinkCB/CN, the transmitting device may be STA1 1702 a, the desired devicemay be AP1 1714 a, and the non-desired device is STA2 1702 b. Incontrast, for the downlink-uplink CB/CN, the transmitting device may beAP2 1714 b, the desired device may be STA2 1702 b, and the non-desireddevice may be AP1 1714 a.

Embodiments for channel information acquisition for downlink-downlinkCB/CN and downlink-uplink CB/CN are described herein. In coordinatedbeamforming or nulling, the transmitting device may need channelfeedback for the channel to both the desired receiver and thenon-desired receiver. For downlink-downlink CB/CN, this channel feedbackinformation may be received from a desired STA and a non-desired STA. Inone example, an AP may send an NDPA/NDP to each STA and request or pollfor feedback from each STA individually. However, for downlinktransmission, a trigger frame based NDPA/NDP procedure may be used toacquire the feedback from each STA in a more efficient manner.

FIG. 18 illustrates an example singling flow 1800 for independentNDPA/NDP and trigger based feedback, which may be used in combination ofany of other embodiments described herein. As illustrated in FIG. 18 ,each AP (e.g., AP1 1814 a and AP2 1814 b) may independently send anNDPA/NDP frame combination (e.g., the combination of NDPA1 1805 and NDP11810, and the combination of NDPA2 1815 and NDP2 1820) to the STAs(e.g., STA1 1802 a, and STA2 1802 b) with independent trigger frames(e.g., a trigger frame 1825, and a trigger frame 1840) to each STA toacquire the feedback (e.g., FB1 1830, FB2 1835, FB1 1845, and FB2 1850).As each STA (e.g., STA1 1802 a, and STA2 1802 b) is associated with bothAPs (e.g., AP1 1814 a and AP2 1814 b), each AP may be able to triggerthe STAs for the feedback (e.g., in an OFDMA manner).

The NDPA frames (e.g., NDPA1 1805 and NDPA2 1815) may indicate the needfor the type of feedback and STA or STAs that should be measuring theNDP frames (e.g., NDP1 1810 and NDP2 1820) to acquire the channel fromthe AP. The NDPA frames (e.g., NDPA1 1805 and NDPA2 1815) may indicatemeasurement and full channel feedback of the channel from the AP to thedesired device. The NDPA frames (e.g., NDPA1 1805 and NDPA2 1815) mayindicate measurement and full channel feedback of the channel from theAP to the non-desired device. The NDPA frames (e.g., NDPA1 1805 andNDPA2 1815) may indicate measurement and partial channel feedback of thechannel from the AP to the non-desired device. Partial information maybe defined as any information that is not the full IEEE 802.11 channelinformation feedback required for the desired channel. The partialchannel feedback may be used to determine a null-space that the designedprecoder should be orthogonal to and, as such, may not need as detailedinformation to improve performance. Examples of partial channel feedbackmay include, but are not limited to, reduced quantization channelfeedback, increased sub-carrier sampling (Ng) channel feedback, channelfeedback based on the channel correlation, and channel feedback based ona sector or codebook.

A trigger frame (e.g., a trigger frame 1825 or a trigger frame 1840)from each AP may indicate the manner in which the feedback (e.g., FB11830, FB2 1835, FB1 1845, and FB2 1850) from each receiving device issent to the announcer. The feedback (e.g., FB1 1830, FB2 1835, FB1 1845,and FB2 1850) may be separated by frequency (e.g., OFDMA), time (e.g.,time staggered), or space (e.g. uplink MU-MIMO). In this case, each APmay independently request information from each STA.

FIG. 19 illustrates an example 1900 of master trigger based NDPA/NDP andmaster trigger based feedback, which may be used in combination of anyof other embodiments described herein. As illustrated in FIG. 19 , amaster AP (e.g., AP1 1914 a) may send an NDPA trigger frame 1905 to asecondary/slave AP (e.g., AP2 1914 b) and both STAs 1902 a, 1902 b toindicate the start of an NDP measurement campaign. Both APs 1914 a, 1914b may send NDP frames (e.g., NDP1 1910 and NDP2 1915) to the STAs 1902a, 1902 b. The NDPs (e.g., NPD1 1910 and NDP2 1915) may be separable atthe STAs 1902 a, 1902 b. The NDPs (e.g., NPD1 1910 and NDP2 1915) may besent at different times. For example, AP1 1914 a sends NDP1 1910, andthen AP2 1914 b sends NDP2 1915. The NDPs (e.g., NPD1 1910 and NDP21915) may be sent at the same time but using different sub-carriers. Inone example, both AP1 1914 a and AP2 1914 b may set Ng=x (e.g.,determined by the NDPA trigger frame 1905), but offset in such a mannerthat there is no overlap. For example, with Ng=4, AP1 1914 a may usesubcarrier indices 0, 4, . . . , while AP2 1914 b may use subcarrierindices 2, 6, . . . . This may require tight synchronization (similar tojoint precoding) between AP1 1914 a and AP2 1914 b to ensure that thereis no frequency, time or synchronization offset at the received STAs1902 a, 1902 b. The master AP (e.g., AP1 1914 a) may send a triggerframe 1920 to both STAs 1902 a, 1902 b and the slave AP (e.g., AP2 1914b) to feed back the desired and undesired information to both APs 1914a, 1914 b. For example, STA1 1902 a may send FB1 1925 to AP1 1914 a andSTA2 1902 b may send FB2 1930 to AP2 1914 b.

For scenarios where there may be a cluster of AP-STA groups, such as 3APs and 3 STAs, this operation may be implemented in a pairwise mannerwhere only two APs/STAs may be allowed to transmit simultaneously.Additionally or alternatively, a single directed, and two non-desired,feedback packets may be sent with the precoder designed to operate inthe null space of the two non-desired channels.

FIG. 20 illustrates an example 2000 of an NDP feedback request from anAP, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 20 , AP1 2014 a may send NDPA12005 and NDP1 2010 to AP2 2014 b and both STAs 2002 a, 2002 b toindicate the start of an NDP measurement campaign. Similarly, AP2 2014 bmay send NDPA2 2015 and NDP2 2020 to AP1 2014 a and both STAs 2002 a,2002 b to indicate the start of an NDP measurement campaign. AP1 2014 amay then send a trigger frame 2025 to AP2 2014 b and both STAs 2002 a,2002 b to feedback the desired and undesired information to AP1 2014 a.For example, upon receiving the trigger frame 2025, AP2 2014 b may sendFB3 2030 to AP1 2014 a, STA1 2002 a may send FB1 2035 to AP1 2014 a andSTA2 2002 b may send FB2 2040 to AP1 2014 a. AP2 2014 b may then send atrigger frame 2045 to AP1 2014 a and both STAs 2002 a, 2002 b tofeedback the desired and undesired information to AP2 2014 b. Forexample, upon receiving the trigger frame 2045, AP1 2014 a may send FB32050 to AP2 2014 b, STA1 2002 a may send FB1 2055 to AP2 2014 b and STA22002 b may send FB2 2060 to AP2 2014 b. The example illustrated in FIG.20 that an AP requests feedback from another AP may be used fordownlink-uplink CB/CN.

FIG. 21 illustrates an example 2100 of an NDP trigger for implicitmultiple AP sounding, which may be used in combination of any of otherembodiments described herein. As illustrated in FIG. 21 , a master AP(e.g., AP1 2114 a) may send an NDPA trigger frame 2105 to a secondary orslave AP (e.g., AP2 2114 b) and both STAs 2102 a, 2102 b to indicate thestart of implicit NDP measurement. The STAs 2102 a, 2102 b may send NDPframes (e.g., NDP1 2110 and NDP2 2115) or sounding frames to the APs2114 a, 2114 b so that the APs 2114 a, 2114 b may estimate the uplinkchannel and derive the downlink channel from the uplink channel. Uponreceiving the NDP frames (e.g., NDP1 2110 and NDP2 2115) or soundingframes, the APs 2114 a, 2114 b may respond ACK frames 2120, 2125 to theSTAs 2102 a, 2102 b. For scenarios where there may be a cluster ofAP-STA groups (e.g., three APs and three STAs), the trigger frame mayindicate the start of each uplink STA transmission or may indicate thatthe STAs transmit simultaneously to the APs.

Embodiments for channel information for uplink-uplink CB/CN anduplink-downlink CB/CN are described herein. For uplink-uplink CB/CN,each STA may need to have knowledge of the channel to its desired AP andnon-desired AP. As the trigger frame is used for downlink (i.e. triggersare sent from the AP to the STA), the NDPA/NDP/feedback proceduredescribed in the downlink-downlink CB/CN scenario may need to bemodified. In one example, reciprocity may be used (e.g., the channelobtained during the DL/DL CB/CN at the STA may be suitable for uplink,and the NDPA/NDP procedure described above may be used without any needfor feedback). The NDPA may be used to indicate that the following NDPmay be used for measurement for uplink coordinated beamforming.

FIG. 22 illustrates an example 2200 of independent NDPA/NDP forreciprocity-based UL/UL CB/CN, which may be used in combination of anyof other embodiments described herein. Each of the STAs 2202 a, 2202 bmay obtain the knowledge of the channel to its desired AP andnon-desired AP among the APs 2214 a, AP2 2214 b, for example, itsdownlink CB/CN. As illustrated in FIG. 22 , with the channelinformation, AP1 2214 a may send NDPA1 2205 to STAs 2202 a, 2202 b toindicate that following NDP1 2210 is used for the measurement of theuplink coordinated beamforming. Similarly, AP2 2214 b may send NDPA22215 to STAs 2202 a, 2202 b to indicate that following NDP2 2220 is usedfor the measurement of the uplink coordinated beamforming.

FIG. 23 illustrates an example 2300 of master-trigger-based NDPA/NDP forUL/UL CB/CN, which may be used in combination of any of otherembodiments described herein. As illustrated in FIG. 23 , a master AP(e.g., AP1 2314 a) may send an NDPA trigger frame 2305 to asecondary/slave AP (e.g., AP2 2314 b) and both STAs 2302 a, 2302 b toindicate following NDP frames 2310, 2315 are used for the measurement ofthe uplink coordinated beamforming. Both APs 2314 a, 2314 b may send NDPframes (e.g., NDP1 2310 and NDP2 2315) to the STAs 2302 a, 2302 b. TheNDPs 2310, 22315 may be separable at the STAs 2302 a, 2302 b. The NDPs2310, 2315 may be sent at different times, or at the same time but usingdifferent sub-carriers.

FIG. 24 illustrates an example 2400 of STA-initiated channelacquisition, which may be used in combination of any of otherembodiments described herein. If reciprocity is not applicable, asillustrated in FIG. 24 , STAs 2402 a, 2402 b may initiate the channelacquisition by sending NDPs (e.g., NDP1 2410 and NDP2 2420) to the APs2414 a, 2424 b and requesting feedback from the APs 2414 a, 2414 b inthe case of UL/UL CB/CN. In one example, each STA 2402 a, 2402 b maysend an NDPA 2405, 2415 and NDP 2410, 2420 to the APs 2414 a, 2424 b andrequest feedback 2430, 2435 from the APs 2414 a, 2424 b. Specifically,STA1 2402 a may send NDPA1 2405 to the APs 2414 a, 2424 b to obtain thechannel information and send NDP1 2410 to request feedback from the APs2414 a, 2424 b. Similarly, STA2 2402 b may send NDPA2 2415 to obtain thechannel information and NDP2 2420 to the APs 2414 a, 2424 b to requestfeedback from the APs 2414 a, 2424 b. Alternatively or additionally,each AP 2414 a, 2424 b may send a feedback trigger frame 2425, 2435 orannouncement frame to the STAs 2402 a, 2402 b and provide feedback 2430,2440 with the channel information for the desired and non-desired STA,as illustrated in FIG. 24 .

FIG. 25 illustrates an example 2500 of AP-initiated channel acquisition,which may be used in combination of any of other embodiments describedherein. In a scenario where there may be many STAs, and theSTA-initiated method may result in a lot of overhead, a master AP (e.g.,AP1 2514 a) may trigger the secondary AP (e.g., AP2 2514 b) and all theSTAs (e.g., STA1 2502 a, STA2 2502 b, STA3 2502 c, and STA4 2502 d) inthe joint BSSs to send a series of NDPs (e.g., NDP1 2515, NDP2 2520,NDP3 2525, and NDP42530) to both APs 2514 a, 2514 b. The APs 2414 a,2424 b may send feedback trigger frames 2535, 2545 or announcement frameto the STAs 2502 a, 2502 b, 2502 c, 2502 d and provide feedback 2540,2550 with the desired and non-desired channels to the STAs 2502 a, 2502b, 2502 c, 2502 d, as illustrated in FIG. 25 .

For UL-DL CB/CN, the NDPA may address the non-desired STA and requestfor feedback from the STA at a later time.

As mentioned above, the APs may need to know the DL channel stateinformation (CSI) for all STAs. In embodiments, this may be done usingimplicit DL channel acquisition where, for example, an AP may acquirethe DL channels from the UL channels.

FIG. 26 illustrates an example 2600 of implicit DL channel acquisition,which may be used in combination of any of other embodiments describedherein. As illustrated in FIG. 26 , AP1 2614 a may infer the DL (e.g.,normalized) channel H₁ ^(d) and H₂ ^(d) from the UL (e.g., normalized)channels H₁ ^(u) and H₂ ^(u). AP1 2614 a may broadcast the desiredreceived signal strength (RSS) at its own location via, for example, RSSindication (RSSI) through a trigger frame STA1 2602 a and STA2 2602 bmay set their transmit powers, P₁ and P₂, respectively, based on theRSSI. This may enable mitigating the inter-cell interference (ICI) dueto carrier frequency offset (CFO) differences under near-far scenarios.In this scenario, the received signal at AP1 2614 a may be expressed as:

${y_{1} = {{{\underset{\ell_{1}}{\underset{︸}{\alpha_{1}P_{1}}}H_{1}^{u}x_{1}} + {\underset{\ell_{2}}{\underset{︸}{\alpha_{2}P_{2}}}H_{2}^{u}x_{2}}} = {\begin{bmatrix}H_{1}^{u} & H_{2}^{u}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}}}},$where x₁ and x₂ are the transmitted symbols with unity power, α₁ and α₁are path loss coefficients, and −

₁=

₂ because of the power setting at STAs 2602 a, 2602 b to achieve desiredidentical RSSs. AP1 2614 a may learn the DL channels from the ULchannels as:[H ₁ ^(d) H ₂ ^(d)]^(H) =[H ₁ ^(u) H ₂ ^(u)]^(H).Since power setting may cause the RSSs to be identical, the relativepath loss information may be lost. On the other hand, the optimalbeamforming vectors for various purposes, such as CB/CN, AP1 2614 a mayneed the matrix given by:

$\begin{bmatrix}H_{1}^{u} & {\frac{\alpha_{1}}{\alpha_{2}}H_{2}^{u}}\end{bmatrix}^{H},$which may be a function of relative path loss,

$\frac{\alpha_{1}}{\alpha_{2}}.$

To obtain α₁ and α₂ or α₁/α₂, the STAs 2602 a, 2602 b may use adeterministic power (e.g., maximum power) or power spectral density(e.g., power per Hz or power per 26 tone RU) in the UL to respond to thechannel acquisition frame (e.g., NDP, NDPA or trigger frame) transmittedfrom AP1 2614 a. The value of the deterministic power or power spectraldensity, if not maximum power, may be signaled in the channelacquisition frame. In this case, since all STAs 2602 a, 2602 b maytransmit a signal using the same power, the pass losses can be measuredat APs (including AP1 2614 a).

The STAs 2602 a, 2602 b may report their maximum power via a MAC frame,such as an association or setup frame. If STAs 2602 a, 2602 b are powercontrolled (e.g., they may use different transmit power), the STAs 2602a, 2602 b may indicate their transmit power or transmit power spectraldensity via PHY signaling, such as in one of the PHY headers, such asthe SIG fields, or through a MAC frame while transmitting a UL PPDU. TheSTAs 2602 a, 2602 b may indicate their power headroom via PHY signaling,such as in in one of the PHY headers, such as the SIG fields, or througha MAC frame while transmitting a UL PPDU. If the channel acquisitionsignal from the APs (including AP1 2614 a) includes the transmit powerused at the APs (including AP1 2614 a), the STAs 2602 a, 2602 b maygenerate the DL pass losses from different APs and feed them back to theAPs (including AP1 2614 a) using a UL channel or a SIG field.

Embodiments for mesh sounding procedures are described herein. Latencyin the network may be reduced by enabling UL and DL at the same timethrough multiple APs distributed in area. FIG. 27 illustratesinterference in an example scenario 2700 for simultaneous UL and DLtraffic, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 27 , the traffic between AP12714 a and STA1 2702 a is UL. The traffic between AP2 2714 b and STA22702 b is DL. AP2 2714 b may interfere with AP1 2714 a, and STA1 2702 amay interfere with STA2 2702 b. To mitigate the interference, CB/CN maybe used, but the AP1-AP2 channel at AP2 2714 b, and the STA1-STA2channel at STA1 2702 a may need to be identified.

To address this, an AP/STA that desires to transmit information (alsoreferred to as an initiator) may transmit a mesh sounding trigger (MST)frame. The MST frame may include the participants in the mesh (e.g.,association IDs or MAC addresses). The MST frame may also include therole of each STA in the upcoming concurrent transmissions. For example,in FIG. 27 , STA1 2702 a and AP2 2714 b may be transmitting STAs, andAP1 2714 a and STA2 2702 b may be receiving STAs. Transmitting STAs mayneed to null to mitigate the interference to the undesired receiving STAor STAs. The MST frame may include a transmission order field that mayexplicitly indicate the transmission order of the sounding frames. Insome embodiments, this may be implicitly indicated by the STA roles.

The participant STAs/APs may access the medium via CSMA protocol andtransmit NDP frames. The NDP frames may be transmitted through differentSTAs/APs sequentially in time. In some embodiments, STAs may accesssimultaneously via orthogonal channel estimation fields.Non-transmitting STAs/APs may use the received NDP to estimate thechannel between the transmitting STA and themselves. Further,non-transmitting STAs/APs may set their MIMO precoding vectors tominimize the interference while ensuring beamforming toward the desiredAPs/STAs.

The initiator AP/STA may then transmit a mesh data trigger (MDT) frame.The MDT frame may include the participant STAs (e.g., their associationIDs), which may join data transmission and the duration for datatransmission, in the next frame. The MDT frame may include the role ofeach STA in the upcoming concurrent transmissions. For example, in FIG.27 , STA1 2702 a and AP2 2714 b may be transmitting STAs, and AP1 2714 aand STA2 2702 b may be receiving STAs. Transmitting STAs may need tonull to mitigate the interference to the undesired receiving STA(s). Theparticipant STAs may receive the MDT. If their AID is indicated, theymay be allowed to transmit data via PPDUs. The initiator AP/STA and theSTAs indicated in MDT may transmit data simultaneously. The OFDM symbolsin the PPDUs may be aligned in time to minimize the interference.

FIG. 28 illustrates example utilization 2800 of MDT and MST frames toCB/CN, which may be used in combination of any of other embodimentsdescribed herein. In the example illustrated in FIG. 28 , AP2 2814 b isthe initiator and may transmit an MST frame 2805. AP1 2814 a, STA1 2802a, and STA2 2802 b may receive the MST frame 2805 and sequentiallytransmit sounding signals 2810, 2815, 2820, 2825 (e.g., NDPs or PPDUs)with information on the TX signal power. AP2 2814 b may also transmitthe sounding signal 2815. During the sounding signals 2810, 2815, 2820,2825, all receiving STAs (e.g., STA1 2802 a and STA2 2802 b) and APs(e.g., AP1 2814 a) may estimate the channel and adjust their beamformingvectors. AP2 2814 b may then transmit an MDT trigger frame 2830, whichmay allow STA1 2802 a to transmit. STA1 2802 a and AP2 2918 b may thentransmit their data through synchronous PPDUs. Since they adjusted theirbeamforming vectors (e.g., CB/CN), STA1 2802 a and AP2 2814 b maymitigate the interference on AP1 2814 a and STA2 2802 b, respectively.

FIG. 29 illustrates an example 2900 of uplink-uplink CB/CN usingone-sided spatial reuse parameter (SRP) based spatial reuse (SR), whichmay be used in combination of any of other embodiments described herein.An SR STA that receives the SRP information may incorporate a precoderinto its SR transmission to lower the overall interference and transmitin a one-sided SR. For example, as illustrated in FIG. 29 , theone-sided SR may imply that STA1 2902 a transmits normally while STA22902 b performs CB/CN to limit the interference to AP1 2914 a during thetransmission.

The STA may incorporate the gain/null of the beamformer into the SRPinterference estimation. The maximum interference estimation in IEEE802.11ax assumes an omni-directional antenna with a gain of 0 dB. TheSTA may then compensate for the nulling effect of the precoder in itsestimation of the interference that will reach the non-desired AP, suchas AP1. The SRP input may then become:SRP_INPUT=TXPWRAP−SCMA_gain+Acceptable Receiver InterferenceLevelAP−(AP2), where SCMA_gain may be estimated by the WTRU using SCAgain estimation types 1 and 2.

FIG. 30 illustrates an example 3000 of sparse code multiple access(SCMA) gain estimation type 1, which may be used in combination of anyof other embodiments described herein. AP1 3014 a may send anannouncement 3005 that there will be a CB/CN gain estimation andindicate the STAs 3002 a, 3002 b to be tested and the APs 3014 a, 3014 bto be tested against. Each STA 3002 a, 3002 b may send an SCMA packetusing the omni-directional antenna 3010, 3020 and the precoder antenna3015, 3025 obtained from estimating the CB/CN precoder, as illustratedin FIG. 30 . The STAs 3002 a, 3002 b may then receive a trigger frame3030 indicating that the gain feedback 3035 will be sent. The gainfeedback 3035 may be the RSSI difference between the received power ofthe frames transmitted with the two antennas. The gain feedback 3035 maybe the RSSI received for each antenna. In this case, the STAs 3002 a,3002 b may estimate the SCMA gain. The STAs 3002 a, 3002 b may receive(or estimate) the SCMA gain from the feedback.

FIG. 31 illustrates an example 3100 of SCMA gain estimation type 2,which may be used in combination of any of other embodiments describedherein. As illustrated in FIG. 31 , AP1 3114 a may send an announcement3105 that there will be a CB/CN gain estimation and indicate the STAs3102 a, 3102 b to be tested and the APs 3114 a, 3114 b to be testedagainst. The STAs 3102 a, 3102 b may all transmit using theomni-directional antennas 3110, 3115 and then switch to the directionalprecoders 3120, 3125 to limit the need for fast switching of the antennabeams, as illustrated in FIG. 31 . The STAs 3102 a, 3102 b may thenreceive a trigger frame 3130 indicating that the gain feedback 3135 willbe sent. The gain feedback 3135 may be the RSSI difference between thereceived power of the frames transmitted with the two antennas. The gainfeedback 3135 may be the RSSI received for each antenna. In this case,the STAs 3102 a, 3102 b may estimate the SCMA gain. The STAs 3102 a,3102 b may receive (or estimate) the SCMA gain from the feedback.

FIG. 32 illustrates an example 3200 of uplink-uplink two sided SRP basedSR, which may be used in combination of any of other embodimentsdescribed herein. In the example illustrated in FIG. 32 , as thenon-desired receiver (e.g., AP2 3214 b) is known, the SRP trigger fromAP1 3214 a may include information on the candidate coordinating APs(e.g., AP2 3214 b) in the trigger frame to STA1 3202 a to enable STA13202 a to design a precoder to limit its interference on itstransmission. This may enable two-sided UL/UL CB/CN.

FIG. 33 illustrates an example 3300 of one-sided DL/UL CB/CN with aprimary UL/DL transmission, which may be used in combination of any ofother embodiments described herein. In the example illustrated in FIG.33 , if the UL transmission from STA1 3302 a to AP1 3314 a is theprimary transmission, the secondary AP (i.e. AP2 3314 b) may elect totransmit to its STA (i.e. STA2 3302 b) while limiting the interferenceto AP1 3314 a. In this case, it may be necessary for the secondary AP(i.e. AP2 3314 b) to request information feedback from the primary AP(i.e. AP1 3314 a) as described above. The secondary STA (i.e. STA2 3302b) may also send an ACK to AP2 3302 b to verify that it may receiveinformation in the presence of the interference from STA1 3302 a. TheACK may be transmitted to AP2 3314 b with a precoder that limitsinterference to AP1 3314 a.

Embodiments for coordinated beamforming for DL/DL or DL/UL architecturesare described herein. For DL/DL CB/CN, if the interference offered tothe interferee is known, one of a number of different methods may beused.

In one embodiment, the AP may send a CB/CN trigger to indicate that theSTA need to send out its interference level. The target STA may respondwith a tolerated interference level. It may send the interference leveltolerated on a 20 MHz channel. Alternatively or additionally, it maysend out its interference level using a per RU granularity. The AP maythen send a downlink transmission. It may be optional as to whether toinclude interference levels. This may allow the listening STAs toestimate the relative interference level to the AP. The neighboring APmay use the information on the identified STA to set the precoder andtransmit power based on the tolerated interference level. This may beone sided as the AP1 may not adjust its transmit precoder to accommodatethe recipient STA for AP2. In a two-sided example, the AP may sendinformation to STA 1 using a precoder that limits interference towardBSS2 (e.g., using a wide angle null space). Alternatively oradditionally, the APs may exchange information on the desired STAsbefore initiating transmission.

In another embodiment, rather than requesting an instantaneousinterference level one STA at a time, the AP may send a request forinterference levels for a set of STAs in the BSS. The AP may send aCB/CN trigger frame to indicate that a set of STAs (e.g., all STAs) needto send out their desired interference levels. The AP may coordinatewith neighboring APs to a have a quiet period during that session. Thetarget STA may respond with a tolerated interference level. It may sendthe tolerated interference level on the 20 MHz channel. Additionally oralternatively, it may send out the interference level using a per RUgranularity. The AP may then send a downlink transmission. It may beoptional whether to include interference levels. This may allow thelistening STAs to estimate the relative interference level to the AP.The neighboring AP may use the information on the identified STA to setthe precoder and transmit power based on the tolerated interferencelevel.

In another embodiment, for DL/UL primary with UL/DL secondary, AP1 maytransmit to a STA (e.g., STA1) in its BSS with a limit on theinterference to AP2. All STAs in BSS1 may send out their interferencelevels. STAs in BSS2 may compete and transmit information to AP1. Thetransmitter may have to get the channel to each STA, as mentioned above.

Embodiments for interference alignment (IA) procedures are describedherein.

FIG. 34 illustrates an example 3400 of multiple master triggering, whichmay be used in combination of any of other embodiments described herein.As illustrated in FIG. 34 , AP1 3414 a may transmit an IA trigger frame(IATF) for AP2 3414 b to transmit with an IA scheme in the upcomingtransmissions. AP2 3414 b may receive the IATF 3405 and understand thatit will be part of IA transmission in the upcoming transmission. AP23414 b may use V₂ for STA2 3402 b as it is triggered. In one example,the IATF 3405 may indicate the interference basis used at the STAs(e.g., STA1 3402 a and STA2 3402 b). AP2 3414 b may calibrate itscarrier frequency to compensate for the potential frequency mismatchbetween them.

Upon receiving the IATF 3405, AP2 3414 b may transmit an ACK (i.e. IAready ACK frame 3410) that acknowledges AP1 3414 a for IA transmission.AP2 3414 b may enter a state in which it waits for ACKs from the STAs3402 a, 3402 b for transmission. AP1 3414 a may then transmit an IATF3415 for STA1 3402 a and STA2 3402 b. STA1 3402 a and STA2 3402 b mayreceive the IATF 3415, determine that they are the recipients, andunderstand that IA transmission will occur. STA1 3402 a and STA2 3402 bmay determine their interference bases as V₁ and V₂, respectively. Theinformation may be in the IATF 3415. STA1 3402 a and STA2 3402 b maycalibrate their carrier frequency to compensate the potential frequencymismatches. AP1 3414 a may enter a state that waits for ACKs from theSTAs 3402 a, 3402 b for transmission for the next transmission

STA1 3402 a and STA2 3402 b may concurrently transmit ACKs (i.e. IAready ACKs 3420, 3425) that may indicate that they are ready for IA andtrigger IA transmission. AP1 3414 a and AP2 3414 b may have M≥3antennas. Hence, they may decode the ACKs 3420, 3425 from up to 3different transmitters. AP1 3414 a and AP2 3414 b may use the channelestimate to construct the IA precoders. AP1 3414 a and AP2 3414 b may betriggered for IA transmission in the next PPDU.

AP1 3414 a and AP2 3414 b may precode and transmit the information (i.e.IA transmissions 3430, 3435) based on an IA scheme. STA1 3402 a and STA23402 b may transmit the ACKs (i.e. IA received ACKs 3440, 3445) toindicate that they received the packets (i.e. IA transmissions 3430,3435). STA1 3402 a may discard the interference on the subspace spannedby the columns of V₁ and decode the rest of the subspace. STA2 3402 bmay discard the interference on the subspace spanned by the columns ofV₂ and decode the rest of the subspace. ACKs may be transmitted on RUsdifferent from RUs used for IA transmission by considering an OFDM-basedsystem.

FIG. 35 illustrates an example 3500 of sequential triggering, which maybe used in combination of any of other embodiments described herein. Asillustrated in FIG. 35 , AP1 3514 a transmits an IA trigger frame (IATF)3505 for AP 23514 b to transmit with IA scheme in the upcomingtransmissions. AP2 3514 b may receive the IATF 3505 and understand thatit will be part of IA transmission in the upcoming transmission. AP23514 b may use V₂ for STA2 3502 b as it is triggered. In anotherembodiment, the IATF 3505 may indicate the interference basis used atthe STAs 3502 a, 3502 b. AP2 3514 b may calibrate its carrier frequencyto compensate the potential frequency mismatch between them.

AP2 3514 b may transmit an IA ACK & trigger frame (IATF-AT) 3510 thatindicates ACK for AP1 3514 a and trigger for STA1 3502 a and STA2 3502b. AP1 3514 a may then enter a state in which it waits for ACKs from theSTAs 3502 a, 3502 b for transmission. STA1 3502 a and STA2 3502 b mayreceive the IATF-AT 3510, determine that they are the recipients, andunderstand that IA transmission will occur. STA1 3502 a and STA2 3502 bmay determine their interference bases as V₁ and V₂, respectively. Theinformation may be in the IATF-AT frame 3510. STA1 3502 a and STA2 3502b may calibrate their carrier frequency to compensate the potentialfrequency mismatch among them. AP2 3514 b may then enter a state inwhich it waits for ACKs from the STAs 3502 a, 3502 b for transmissionafter the transmission.

STA1 3502 a and STA2 3502 b may concurrently transmit ACKs (i.e. IAready ACKs 3515, 3520) that may indicate that they are ready for IA andtrigger IA transmission. AP1 3514 a and AP2 3514 b may have M≥3antennas. Hence, they may decode the ACKs 3515, 3520 from up to 3different transmitters. AP1 3514 a and AP2 3514 b may use the channelestimate to construct the IA precoders. AP1 3514 a and AP2 3514 b may betriggered for IA transmission in the next PPDU.

AP1 3514 a and AP2 3514 b may precode and transmit the information (i.e.IA transmissions 3525, 3530) based on an IA scheme. STA1 3502 a and STA23502 b may transmit the ACK (i.e. IA received ACKs 3535, 3540) toindicate that they received the packets (i.e. IA transmissions 3525,3530). STA1 3502 a may discard the interference on the subspace spannedby the columns of V₁ and decode the rest of the subspace. STA2 3502 bmay discard the interference on the subspace spanned by the columns ofV₂ and decode the rest of the subspace. ACKs may be transmitted on RUsdifferent than the RUs used for IA transmission by considering anOFDM-based system.

FIG. 36 illustrates an example 3600 of pre-sounding-based mastertriggering, which may be used in combination of any of other embodimentsdescribed herein. As illustrated in FIG. 36 , AP1 3614 a transmits an IAtrigger frame (IATF) 3605 for AP2 3614 b to transmit and for STA1 3602 aand STA2 3602 b to receive with the IA scheme in the upcomingtransmissions. AP2 3614 b, STA1 3602 a, and STA2 3602 b may receive theIATF 3605 and understand that IA transmission will occur. AP2 3614 b maydetermine that it will be part of the IA transmission in the upcomingtransmission. AP2 3614 b may use V₂ for STA2 3602 b as it is triggered.In one example, the IATF 3605 may indicate the interference basis usedat the STAs 3602 a, 3602 b. STA1 3602 a and STA2 3602 b may determinethat they are the recipients. STA1 3602 a and STA2 3602 b may determinetheir interference bases as V₁ and V₂, respectively. AP2 3614 b, STA13602 a, and STA2 3602 b may calibrate their carrier frequency tocompensate the potential frequency mismatch among them.

AP2 3614 b, STA1 3602 a, and STA2 3602 b may concurrently transmit ACKframes (i.e. IA ready ACKs 3610, 3615, 3620), which may indicate thatthey are ready for IA and trigger IA transmission. AP1 3614 a may haveM≥3 antennas. Hence, AP1 3614 a may decode the ACKs (i.e. IA ready ACKs3610, 3615, 3620) from 3 different transmitters, such as AP2 3614 b,STA1 3602 a, and STA2 3602 b. AP1 3614 a and AP2 3614 b may precode andtransmit the information (i.e. IA transmissions 3625, 3630) based on anIA scheme. STA1 3602 a and STA2 3602 b may transmit the ACKs (i.e. IAreceived ACKs 3635, 3640) to indicate that they received the packets(i.e. IA transmissions 3625, 3630). STA1 3602 a may discard theinterference on the subspace spanned by the columns of V₁ and decode therest of the subspace. STA2 3602 b may discard the interference on thesubspace spanned by the columns of V₂ and decode the rest of thesubspace. ACKs may be transmitted on RUs different than the RUs used forIA transmission by considering an OFDM-based system.

Embodiments for precoding for channel estimation field for interferencealignment (IA) are described herein. In embodiments, in matrix form, thetransmitted signals from AP1 and AP2 and the received signals at STA1and STA2 may be expressed as:

$t_{1} = {\begin{bmatrix}{H_{21}^{- 1}V_{2}} & {H_{11}^{- 1}V_{1}}\end{bmatrix}\begin{bmatrix}a_{1} \\b_{1}\end{bmatrix}}$ ${t_{2} = {\begin{bmatrix}{H_{22}^{- 1}V_{2}} & {H_{12}^{- 1}V_{1}}\end{bmatrix}\begin{bmatrix}a_{2} \\b_{2}\end{bmatrix}}},$$r_{1} = {\underset{H_{{sta}_{1}}}{\underset{︸}{\begin{bmatrix}{H_{11}H_{21}^{- 1}V_{2}} & {H_{12}H_{22}^{- 1}V_{2}} & V_{1}\end{bmatrix}}}\begin{bmatrix}a_{1} \\a_{2} \\{b_{1} + b_{2}}\end{bmatrix}}$ and${r_{2} = {\underset{H_{{sta}_{2}}}{\underset{︸}{\begin{bmatrix}{H_{21}H_{11}^{- 1}V_{1}} & {H_{22}H_{12}^{- 1}V_{1}} & V_{2}\end{bmatrix}}}\begin{bmatrix}b_{1} \\b_{2} \\{a_{1} + a_{2}}\end{bmatrix}}},$where H_(sta) ₁ and H_(sta) ₂ are the channel matrices that may beneeded to decode the information. To enable the estimation of H_(sta)_(1 and H) _(sta) ₂ , the LTF may be expanded (e.g., multiple LTFtransmission with different α₁, α₂, b₁, and b₂) considering the factthat the information symbols for one station do not come from the sameAP in the IA scheme. In one embodiment, AP1 and AP2 may transmitmultiple signals based on joint design, which may yield to theorthogonal channel estimation matrices at the receive sides. In otherwords, the transmission scheme at AP1 and AP2 may cause two orthogonalmatrices when the signals reach to the receivers. For example, considerthe following expansions:

1^(st) transmission: a₁=1_(M/3), a₂=0_(M/3), b₁=1_(M/3) and b₂=0_(M/3),where 1_(M/3) and 0_(M/3) is an all one and zero column vectors oflength M/3, respectively. This choice may lead to the following vectorsat the STA1 and STA2, respectively:

$\begin{bmatrix}a_{1} \\a_{2} \\{b_{1} + b_{2}}\end{bmatrix} = {{\begin{bmatrix}1_{M/3} \\0_{M/3} \\1_{M/3}\end{bmatrix}{{and}\begin{bmatrix}b_{1} \\b_{2} \\{a_{1} + a_{2}}\end{bmatrix}}} = \begin{bmatrix}1_{M/3} \\0_{M/3} \\1_{M/3}\end{bmatrix}}$

2^(nd) transmission: a₁=1_(M/3), a₂=0_(M/3), b₁=−1_(M/3), andb₂=0_(M/3). This choice may lead to the following vectors at the STA1and STA2, respectively:

$\begin{bmatrix}a_{1} \\a_{2} \\{b_{1} + b_{2}}\end{bmatrix} = {{\begin{bmatrix}1_{M/3} \\0_{M/3} \\{- 1_{M/3}}\end{bmatrix}{{and}\begin{bmatrix}b_{1} \\b_{2} \\{a_{1} + a_{2}}\end{bmatrix}}} = \begin{bmatrix}{- 1_{M/3}} \\0_{M/3} \\1_{M/3}\end{bmatrix}}$

3^(rd) transmission: a₁=0_(M/3), a₂=0_(M/3), b₁=0_(M/3), and b₂=√{squareroot over (2)}×1_(M/3). This choice leads to the following vectors atthe STA1 and STA2, respectively:

$\begin{bmatrix}a_{1} \\a_{2} \\{b_{1} + b_{2}}\end{bmatrix} = {{\begin{bmatrix}0_{M/3} \\0_{M/3} \\{\sqrt{2} \times 1_{M/3}}\end{bmatrix}{{and}\begin{bmatrix}b_{1} \\b_{2} \\{a_{1} + a_{2}}\end{bmatrix}}} = \begin{bmatrix}0_{M/3} \\{\sqrt{2} \times 1_{M/3}} \\0_{M/3}\end{bmatrix}}$

At the end of 3^(rd) transmission, the information transmitted at AP1,AP2, STA1 and STA2, where each column is associated with differenttransmission instants (a₁(i) is the ith transmission instant), may begiven by:

$P^{{AP}_{1}} = {\begin{bmatrix}{a_{1}(1)} & {a_{1}(2)} & {a_{1}(3)} \\{b_{1}(1)} & {b_{1}(2)} & {b_{1}(3)}\end{bmatrix} = \begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} \\1_{M/3} & {- 1_{M/3}} & 0_{M/3}\end{bmatrix}}$ $P^{{AP}_{2}} = {\begin{bmatrix}{a_{2}(1)} & {a_{2}(2)} & {a_{2}(3)} \\{b_{2}(1)} & {b_{2}(2)} & {b_{2}(3)}\end{bmatrix} = \begin{bmatrix}0_{M/3} & 0_{M/3} & 0_{M/3} \\0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}}\end{bmatrix}}$ $P^{{STA}_{1}} = \begin{bmatrix}{a_{1}(1)} & {a_{1}(2)} & {a_{1}(3)} \\{a_{2}(1)} & {a_{2}(2)} & {a_{2}(3)} \\{{b_{1}(1)} + {b_{2}(1)}} & {{b_{1}(2)} + {b_{2}(2)}} & {{b_{1}(3)} + {b_{2}(3)}}\end{bmatrix}$ $= \begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} \\0_{M/3} & 0_{M/3} & 0_{M/3} \\1_{M/3} & {- 1_{M/3}} & {\sqrt{2} \times 1_{M/3}}\end{bmatrix}$ and $P^{{STA}_{2}} = \begin{bmatrix}{b_{1}(1)} & {b_{1}(2)} & {b_{1}(3)} \\{b_{2}(1)} & {b_{2}(2)} & {b_{2}(3)} \\{{a_{1}(1)} + {a_{2}(1)}} & {{a_{1}(2)} + {a_{2}(2)}} & {{a_{1}(3)} + {a_{2}(3)}}\end{bmatrix}$ $= {\begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} \\0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}} \\1_{M/3} & {- 1_{M/3}} & 0_{M/3}\end{bmatrix}.}$

While P^(STA) ² may be an orthogonal matrix, P^(STA) ¹ may not be anorthogonal matrix. Both STAs may estimate the channels H_(sta) ₁ andH_(sta) ₂ . However, STA2's estimation may be more reliable than STA1'sestimation since P_(sta) ₁ is an orthogonal matrix. To be fair to bothstations in terms of channel estimation, a 4th transmission may occur:

4^(th) transmission: a₁=0_(M/3) a₂=√{square root over (2)}×1_(M/3)b₁=0_(M/3) and b₂=0_(M/3). This choice may lead to the following vectorsat the STA1 and STA2, respectively:

$\begin{bmatrix}a_{1} \\a_{2} \\{b_{1} + b_{2}}\end{bmatrix} = {{\begin{bmatrix}0_{M/3} \\{\sqrt{2} \times 1_{M/3}} \\0_{M/3}\end{bmatrix}{{and}\begin{bmatrix}b_{1} \\b_{2} \\{a_{1} + a_{2}}\end{bmatrix}}} = \begin{bmatrix}0_{M/3} \\0_{M/3} \\{\sqrt{2} \times 1_{M/3}}\end{bmatrix}}$

At the end of the 4^(th) transmission, the expansion matrices at AP1,AP2, STA1 and STA 2, where each column is associated with thetransmission index, may be given by:

$P^{{AP}_{1}} = \begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} & 0_{M/3} \\1_{M/3} & {- 1_{M/3}} & 0_{M/3} & 0_{M/3}\end{bmatrix}$ $P^{{AP}_{2}} = \begin{bmatrix}0_{M/3} & 0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}} \\0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}} & 0_{M/3}\end{bmatrix}$ $P^{{STA}_{1}} = \begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} & 0_{M/3} \\0_{M/3} & 0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}} \\1_{M/3} & {- 1_{M/3}} & {\sqrt{2} \times 1_{M/3}} & 0_{M/3}\end{bmatrix}$ and $P^{{STA}_{2}} = {\begin{bmatrix}1_{M/3} & 1_{M/3} & 0_{M/3} & 0_{M/3} \\0_{M/3} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}} & 0_{M/3} \\1_{M/3} & {- 1_{M/3}} & 0_{M/3} & {\sqrt{2} \times 1_{M/3}}\end{bmatrix}.}$

Since the 1^(st), 2^(nd), and 4^(th) transmissions may lead to anorthogonal matrix STA1's estimation, the channel estimation quality atSTA1 may be improved.

FIG. 37 illustrates an example LTF construction 3700 for AP1 and AP2 forIA, which may be used in combination of any of other embodimentsdescribed herein. In the example illustrated in FIG. 37 , s_(i) is anelement of the long training field (LTF) sequence (e.g., IEEE 802.11legacy LTF), P_(kl) ^(AP) ¹ is an element of P^(AP) ¹ , and P_(kl) ^(AP)² is an element of P^(AP) ² . To achieve similar power distribution atboth AP1 3714 a and AP2 3714 b, the rows and columns P^(AP) ¹ and P^(AP)² may alternate for different subcarriers and OFDM symbol indices.

In another example, AP1 and AP2 may share the row of a genericorthogonal expansion matrix. For example, assume that the genericexpansion matrix P matrix is given by:

$P = \begin{bmatrix}1 & 1 & 1 & {- 1} \\1 & {- 1} & 1 & 1 \\1 & 1 & {- 1} & 1 \\1 & {- 1} & {- 1} & {- 1}\end{bmatrix}$

P^(AP) ¹ may be the first two rows of P matrix, and P^(AP) ¹ may be thelast two rows of P matrix. The matrices may only be about generatingorthogonal streams, and the IA precoder may expand it to the antennas.In that case, STA1 may estimate H_(sta) ₁ by using the rows of Passociated with a₁, a₂ for the first and the second useful streams(e.g., the first row of P is for the first stream transmitted from AP1and the third row of P is for the second stream transmitted from AP2),and one of the rows of P associated b₁ or b₂ for the interferencesubspace V₁. Similarly, the STA2 may estimate H_(sta) ₂ by using therows of P associated with b₁, b₂ for the first and the second usefulstreams (e.g., the second row of P is for the first stream transmittedfrom AP1 and the fourth row of P is for the second stream transmittedfrom AP2) and one of the rows of P associated a₁ or a₂ for theinterference subspace V₂. As a numerical example, it is assumed thatr_(1,2,3,4) ^(STA) ¹ and r_(1,2,3,4) ^(STA) ² are the observationvectors at STA 1 and STA 2 for one subcarrier for 4 OFDM symbols basedon the aforementioned P matrix. H_(sta) ₁ and H_(sta) ₂ may be obtainedas:

$H_{{sta}_{1}} = {{\frac{1}{4}\begin{bmatrix}r_{1}^{{STA}_{1}} & r_{2}^{{STA}_{1}} & r_{3}^{{STA}_{1}} & r_{4}^{{STA}_{1}}\end{bmatrix}}\begin{bmatrix}1 & 1 & 1 & {- 1} \\1 & 1 & {- 1} & 1 \\1 & {- 1} & 1 & 1\end{bmatrix}}^{H}$ $H_{{sta}_{2}} = {{\frac{1}{4}\begin{bmatrix}r_{1}^{{STA}_{1}} & r_{2}^{{STA}_{1}} & r_{3}^{{STA}_{1}} & r_{4}^{{STA}_{1}}\end{bmatrix}}\begin{bmatrix}1 & {- 1} & 1 & 1 \\1 & {- 1} & {- 1} & {- 1} \\1 & 1 & 1 & {- 1}\end{bmatrix}}^{H}$

Embodiments for power enhanced implicit sounding are described herein.An AP may be able to transmit with higher power than the STA. Withexplicit sounding, the AP may transmit the sounding packet withrelatively higher power as compared to the STA. The STA may performchannel estimation and then quantize the channel information and send itback to the AP. With implicit sounding, the STA may be able to transmitthe sounding packet with a relatively lower power as compared to the AP,and the AP may perform channel estimation. The channel estimation basedon the DL sounding frame may be more accurate than channel estimationbased on the UL sounding frame due to the transmission power difference.Embodiments are described below that may compensate the transmissionpower difference between the AP and the STA.

To generalize, in the case that the device transmitting the NDP (eitherthe AP or the STA) in the implicit channel acquisition is power limited,the device may autonomously modify its NDP transmission to improve thechannel estimate or receive signaling from the receiver to modify itsNDP transmission to improve the channel estimate. It may improve itschannel estimate by one or more of the following methods restricting thebandwidth of the NDP (e.g., an RU) and boosting the power it transmitswithin the restricted bandwidth and changing the sounding duration(e.g., transmitting multiple repetitions of the NDP signal to increasethe number of pilots/reference signals from which the channel isestimated).

For the case of UL sounding, in some embodiments, one or more STAs maytransmit a UL sounding sequence in a narrower band (e.g., on a subset ofsubcarriers) so that the power density on each subcarrier may beincreased when the total transmit power remains the same. This may besubject to a total power or power spectral density constraint. In someembodiments, the one or more STAs may transmit a UL sounding sequencewith normal transmit power and power density. However, the UL soundingsequence may repeat several times in time domain so that the one or moreAPs may receive the sounding sequence with better SNR. The repetition ofthe sounding sequence may also be combined with changing the powerspectral density of the signal transmitted.

FIG. 38 illustrates an example multiple AP implicit sounding procedure3800 with a sounding frame, which may be used in combination of any ofother embodiments described herein. As illustrated in FIG. 38 , AP1 3814a may transmit a sounding trigger frame 3805 to the STAs 3802 a, 3802 b.Upon receiving the sounding trigger frame 3805, the STAs 3802 a, 3802 bmay send sounding frames 3810, 3815 to the APs 3814 a, 3814 b. In theexample illustrated in FIG. 38 , a sounding frame 3810, 3815 may carry awideband legacy preamble part 3810 a, 3815 a and an RU based LTF part3810 b, 3815 b. The wideband preamble part 3810 a, 3815 a may carryL-STF, L-LTF, and L-SIG fields and additional SIG fields transmittedusing legacy numerology. This wideband preamble part 3810 a, 3815 a maybe transmitted normally using controlled power or maximum power. For theRU based LTF part 3810 b, 3815 b, the RU may be considered as a basictransmission unit. A STA may transmit one or more RU for LTFtransmissions. Upon receiving the sounding frames 3810, 3815, the APs3814 a, 3814 b may transmit ACK frames 3820, 3825 to the STAs 3802 a,3802 b.

In some embodiments, the STA may transmit one or more RUs in one OFDMsymbol. The RUs may be localized (e.g., adjacent to each other) ordistributed. In some embodiments, the STA may allocate as much power aspossible for the RUs. The STA may transmit more OFDM symbols for channelsounding. In some embodiments, the STA may transmit on the same set ofRUs for all the OFDM symbols.

In one example, as illustrated in FIG. 38 , the STAs 3802 a, 3802 b maytransmit on the different set of RUs for all the OFDM symbols (e.g., asshown in FIG. 38 , the STAs 3802 a, 3802 b may transmit on the samenumber of RUs but shift the RU locations). The RU allocation for eachSTA to transmit its sounding sequence may be indicated in the soundingtrigger frame. The number of OFDM symbols to carry the sounding sequencemay be indicated in the sounding trigger frame. In some embodiments, theSTA transmitting the NDP may transmit multiple NDP frames with eachframe on a different frequency resource or RU with the power andduration needed to ensure proper channel estimation quality on eachresource. In some embodiments, the AP may signal the specific RUs andthe order in which they are to be transmitted on. In one example, the APmay signal a starting RU and ending RU, and the STA transmitting theNDPs may transmit on the RUs in a predetermined order (e.g.,consecutively) until the entire bandwidth is spanned.

If more than one STA may transmit concurrent UL sounding frames, the STAmay be distinguished by P matrix or in the frequency domain. In someembodiments, the AP may signal multiple STAs to transmit their NDPscycled in such a way that each STA spans its desired sounding BW and allSTAs transmit on orthogonal resources.

To perform implicit channel sounding, an AP may need to be calibrated.In some embodiments, the AP may perform self-calibration so that it maynot require non-AP STAs to estimate the channel and send CSI back.

FIG. 39 illustrates an example procedure 3900 for self-calibration,which may be used in combination of any of other embodiments describedherein. The self-calibration may allow non-AP STAs (e.g., STA 3902) toknow the duration of the self-calibration procedure so that the STAs mayset NAV accordingly. In the example illustrated in FIG. 39 , AP1 3914may transmit a CTS-2-Self frame 3905 or other type of control/managementframe with duration field set to cover the time used forself-calibration. Alternatively or additionally, AP1 3914 may transmitthe self-calibration frames 3910, 3915 as part of an aggregated frame tomultiple users (e.g., STA 3902), with the self-calibration sub-frameaddressed to itself. For example, AP1 3914 may send the self-calibrationframes 3910, 3915 to the STA 3902 while the STA 3902 is in NAV 3920.

The AP may transmit one or more self-calibration frames. In someembodiments, the self-calibration frame may be vendor defined and maynot need to be understood by the other STAs in the system. In someembodiments, the self-calibration frame may use a Wi-Fi PPDU format sothe other STAs may know they are Wi-Fi frames. At the end ofcalibration, the AP may transmit a TXOP end frame to indicate thecompletion of the self-calibration. As illustrated in FIG. 39 , non-APSTAs (e.g., STA 3902) may check the CTS-2-self frame 3905 and set NAV3920 accordingly. The STA may also enter power save mode if the AP isthe serving AP for the STA.

Although features and elements are described herein considering IEEE802.11 specific protocols, it may be understood that the solutionsdescribed herein are not restricted to this scenario and are applicableto other wireless systems as well.

Further, although features and elements are described above inparticular combinations, one of ordinary skill in the art willappreciate that each feature or element can be used alone or in anycombination with the other features and elements. In addition, themethods described herein may be implemented in a computer program,software, or firmware incorporated in a computer-readable medium forexecution by a computer or processor. Examples of computer-readablemedia include electronic signals (transmitted over wired or wirelessconnections) and computer-readable storage media. Examples ofcomputer-readable storage media include, but are not limited to, a readonly memory (ROM), a random access memory (RAM), a register, cachememory, semiconductor memory devices, magnetic media such as internalhard disks and removable disks, magneto-optical media, and optical mediasuch as CD-ROM disks, and digital versatile disks (DVDs). A processor inassociation with software may be used to implement a radio frequencytransceiver for use in a WTRU, UE, terminal, base station, RNC, or anyhost computer.

What is claimed is:
 1. A method for use in an IEEE 802.11 station (STA),the method comprising: receiving, from a first access point (AP), aprobe response frame including one or more indicators indicatingmultiple AP operation capabilities of the first AP and a second AP,wherein the first AP and the second AP are included in a multiple APservice set comprising a plurality of APs that are able to support amultiple AP operation; transmitting, to at least one of the first AP orthe second AP, a multiple AP association request frame for the multipleAP operation with the IEEE 802.11 STA, wherein the multiple AP operationincludes reception of signals by the IEEE 802.11 STA from the first APand the second AP; receiving, from the first AP, based on apredetermined order in the multiple AP service set, a first multiple APassociation response frame that indicates acceptance or rejection of themultiple AP operation with the first AP; and receiving, from the secondAP, based on the predetermined order in the multiple AP service set, asecond multiple AP association response frame that indicates acceptanceor rejection of the multiple AP operation with the second AP.
 2. Themethod of claim 1, wherein the multiple AP operation capabilitiescomprise a multiple AP joint transmission capability, a multiple APhybrid automatic repeat request (HARQ) capability, a multiple APmultiple-input multiple-output (MIMO) capability, a dynamic AP selectioncapability, a multiple AP roaming capability, or a multiple APcoordinated beamforming capability.
 3. The method of claim 1, furthercomprising: receiving a second probe response frame from the second AP,wherein on a condition that the first AP and the second AP are not in asame multiple AP service set, the first probe response frame includesone or more indicators indicating multiple AP operation capabilities ofa plurality of APs in a first multiple AP service set associated withthe first AP, and wherein the second probe response frame includes oneor more indicators indicating multiple AP operation capabilities of aplurality of APs in a second multiple AP service set associated with thesecond AP.
 4. The method of claim 1, further comprising: transmitting aprobe request frame including an indication that the IEEE 802.11 STA isable to support the multiple AP operation.
 5. The method of claim 1,further comprising: on a condition that the first multiple APassociation response frame is correctly decoded, transmitting, to thefirst AP, a first multiple AP association acknowledge (ACK) frame; on acondition that the first multiple AP association response frame is notcorrectly decoded, transmitting, to the first AP, a first multiple APassociation negative acknowledge (NACK) frame; on a condition that thesecond multiple AP association response frame is correctly decoded,transmitting, to the second AP, a second multiple AP association ACKframe; and on a condition that the second multiple AP associationresponse frame is not correctly decoded, transmitting, to the second AP,a second multiple AP association NACK frame.
 6. The method of claim 1,further comprising: on a condition that both the first and secondmultiple AP association response frames indicate acceptance, performingthe multiple AP operation with the first AP and the second AP.
 7. Themethod of claim 1, wherein the multiple AP operation with the first APand the second AP is performed using coordinated orthogonalfrequency-division multiple access (OFDMA) or coordinated nulling. 8.The method of claim 1, wherein the multiple AP operation includessimultaneous reception of signals by the IEEE 802.11 STA from the firstAP and the second AP or simultaneous transmission of signals from theIEEE 802.11 STA to the first AP and the second AP.
 9. An IEEE 802.11station (STA) comprising: a receiver configured to receive, from a firstaccess point (AP), a probe response frame including one or moreindicators indicating multiple AP operation capabilities of the first APand a second AP, wherein the first AP and the second AP are included ina multiple AP service set comprising a plurality of APs that are able tosupport a multiple AP operation; a transmitter configured to transmit,to at least one of the first AP or the second AP, a multiple APassociation request frame for the multiple AP operation with the IEEE802.11 STA, wherein the multiple AP operation includes reception ofsignals by the IEEE 802.11 STA from the first AP and second AP; and thereceiver further configured to: receive, from the first AP, based on apredetermined order in the multiple AP service set, a first multiple APassociation response frame that indicates acceptance or rejection of themultiple AP operation with the first AP; and receive, from the secondAP, based on the predetermined order in the multiple AP service set, asecond multiple AP association response frame that indicates acceptanceor rejection of the multiple AP operation with the second AP.
 10. TheIEEE 802.11 STA of claim 9, wherein the multiple AP operationcapabilities comprise a multiple AP joint transmission capability, amultiple AP hybrid automatic repeat request (HARQ) capability, amultiple AP multiple-input multiple-output (MIMO) capability, a dynamicAP selection capability, a multiple AP roaming capability, or a multipleAP coordinated beamforming capability.
 11. The IEEE 802.11 STA of claim9, wherein the receiver is further configured to receive a second proberesponse frame from the second AP, wherein on a condition that the firstAP and the second AP are not in a same multiple AP service set, theprobe response frame includes one or more indicators indicating multipleAP operation capabilities of a plurality of APs in a first multiple APservice set associated with the first AP, and wherein the second proberesponse frame includes one or more indicators indicating multiple APoperation capabilities of a plurality of APs in a second multiple APservice set associated with the second AP.
 12. The IEEE 802.11 STA ofclaim 9, wherein the transmitter is further configured to transmit aprobe request frame including an indication that the IEEE 802.11 STA isable to support the multiple AP operation.
 13. The IEEE 802.11 STA ofclaim 9, wherein the transmitter is further configured to: on acondition that the first multiple AP association response frame iscorrectly decoded, transmit, to the first AP, a first multiple APassociation acknowledge (ACK) frame; on a condition that the firstmultiple AP association response frame is not correctly decoded,transmit, to the first AP, a first multiple AP association negativeacknowledge (NACK) frame; on a condition that the second multiple APassociation response frame is correctly decoded, transmit, to the secondAP, a second multiple AP association ACK frame; and on a condition thatthe second multiple AP association response frame is not correctlydecoded, transmit, to the second AP, a second multiple AP associationNACK frame.
 14. The IEEE 802.11 STA of claim 9, wherein the transmitterand the receiver are further configured to perform, on a condition thatboth the first and second multiple AP association response framesindicate acceptance, the multiple AP operation with the first AP and thesecond AP.
 15. The IEEE 802.11 STA of claim 9, wherein the multiple APoperation with the first AP and the second AP is performed usingcoordinated orthogonal frequency-division multiple access (OFDMA) orcoordinated nulling, and the multiple AP operation includes simultaneousreception of signals by the IEEE 802.11 STA from the first AP and thesecond AP or simultaneous transmission of signals from the IEEE 802.11STA to the first AP and the second AP.